Hi! I'll try to answer some of your questions. It's been about 10 years that I haven't lived in Yukon though...

My first question is related to actually getting myself, the Bicycle and all my gear up to Tuk to start the journey. I understand that I can fly to Inuvik (from Yellowknife I think) and that there are very expensive flights from Inuvik to Tuk.....is there a local transport service between these two towns like a bus that I could use? Is hitching a lift up to the top with locals an option....even though I’ll have my bike?

I very much doubt there is local, overland transport into Tuk. Hitchhiking is a way of life out there - but be prepared for drunk drivers, and long stretches alone. If you hitch - be prepared to do it in increments, and it might take a few days even. You could always ask around about hitching to Tuk (i.e. is it a good idea? What should I expect? etc...) . It's certainly not something to count on. I'd bet a lot of money there's no service to to Tuk that's overland. There is an airline company called Air North based in the Yukon. They don't fly to Tuk but you might try calling them and asking for suggestions on how to get to Tuk. People in these Northern parts are community oriented and it's not uncommon for someone to know someone else who can get you in touch with their cousin who knows a way there... Call transport and delivery companies and airlines and they might put you in touch with someone who knows a way.

Any other suggestions?

Rent a car? Inquiring at a car rental company could be a good idea. Again - if you have the time - hitchhike.

Water, Food and Re-Supply enroute:- Can I count on getting full supplies for my journey in Inuvik and Tuk? In particular food to cover myself for 5-6 days on the road. I’ll be camping as much as I can and obviously cooking my meals as I go. Just the basic staples to get me through that section and snacks etc.

Agree with the above poster - stock up in Inuvik. You'll likely find little stores along the way, but nothing reliable.

I have read some blogs of folks riding the other way and they have had food resupplies sent from Dawson to Eagle Plains.....does anyone know if the same service is offered going in the opposite direction? Would be great to cut down on weight / food carried out of Inuvik :)

Again - nothing reliable that I can think of. If you're willing to pay the price it probably exists. Ask around, stock up when it's reasonably priced, and err on the side of too much vs. too little.

Is it possible to buy Camping Gas (Propane, Butane) in either Inuvik or Tuk - this will help determine the cooking system I’ll bring.

Inuvik yes. Not sure about Tuk. Again - maybe try asking people around town. Someone might have it who's willing to sell it. It's not something to count on - but you could try...

Water:- I’ll bring my water filter and Purification tabs, but are there rivers / streams along that route to resupply from? Is this water drinkable or does it need to be treated first?

So different people might tell you different things - but I personally drink from streams, babbling brooks, lakes, rivers, etc.. that I find along the way. I would argue the water is cleaner than what you get from the tap in most cities. If you esaily get upset stomach - maybe bring purification - but (again - not speaking or everyone) wouldn't.

Am I correct in assuming that food, water and shelter is available at Fort McPherson, Eagle Plains and then Dawson once I start riding south from Inuvik?

I don't know about Eagle Plains - but for the other two - absolutely you can stock up.

What can I expect in terms of cell phone coverage? Wifi availability?

Ask locals - I think generally Bell has the best cell reception in Canada - but google it. Wifi should be available in Dawson. I'd be surprised if Tuk doesn't have any - but it might be spotty.

Mosquitoes:- We have some serious bug action on the west coast of the South Island, NZ but I’ve read that in this region they are huge, plentiful and relentless!! I’ll bring a head net, be able to cover up my body and bring some heavy duty repellent, but are there any other helpful hints or tips you could offer?? I usually make a small, smoky fire if and when I can which also helps.

Mosquitos hate smoke - I've done hikes in the Guatemalan jungle lol and everyone smokes to repel the mosquitoes. Not the recommended method though lol... I've heard citronella is a good repellent. I also knew a fellow who lived out in the bush who swore by some mosquito repellent that was infused with coconut oil lol. Maybe try to find it. Again- don't be shy to ask locals. Maybe bring a spare head-net in case you lose yours.

Bears:- What do I do about the bears.... may sound like a stupid question, but I’ve never dealt with this situation before. Please, apart from keeping all my food and smelly stuff seperate from my campsite, what else should I do....do I need to get bear spray. Do I bag all my food and smelly stuff, seal it and hang it from a tree?? What is the best advice here please?

Bears don't like people. Make a lot of noise. Sing to yourself - carry some bear bells. Don't panic if you see one (you might). Here is a good website: https://www.pc.gc.ca/en/pn-np/mtn/ours-bears/securite-safety/ours-humains-bears-people
Read over it^ and know what to do in case of an encounter. Be prepared but not paranoid. I've encountered many bears in my travel but never had a problem. Bear spray is a good investement and in fact - in some national parks they'll keep bear spray that was left behind by other travelers and they'll let you use it. Bear spray has it's own set of rules (for example - you can't spray it against the wind) - so be sure to read on those limitations.
Bear bangers are another option - they're like firecrackers that make a loud 'BANG' and scare the bear away.
While camping - yes - slung over a rope hanging from a tree is the recommended advice for your food.

Weather Conditons:- No, I’m not asking anyone to predict the weather :) but generally speaking what sort of weather extremes can I expect in the month of July? Can it drop to freezing at the top of the Highway and then get to the mid 20’s after Eagle Plains? I’ll keep definitely cover wet weathers, but wondering how cold nights can get, unexpected snow storms?? Just trying to cover all the bases in terms of a sleeping system and riding gear / kit!

No snowstorms. It could possibly (likely) get uncomfortably cold sometimes. You'll be above the arctic circle - so you'll have some days with no night, or very little night. I don't think it would go to freezing though, even at Tuk. July is the best month to go - so good choice. I'd suggest a good sweater, expect +5C at coldest, GLOVES, hat, and some good wool socks at night.If I was going to do what you do - I'd choose July as well.
Try to find some this:
https://www.google.com/search?q=hand+warmers&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiZuMyfr57gAhUowVkKHSvmB4cQ_AUIDigB&biw=1920&bih=938#imgrc=v-vUPDs4J9h2NM:

This is pretty cool! Send me a PM with an update when you've done it about how it went!
Cheers!

Lucky you going to WA, once there join the secessionist movement. Why are you going via Melbourne from Sydney?, to check out Bleak City before you get to the God Zone? I've done the trip a few times and in no particular order the following come to mind. As you noted, winter means shorter days, and you will be driving into the sunset for the last couple of hours. On the other hand, the clock is set back heading west so you get longer drives. On the subject of time, there is is an un-official central Australian time which operates around Eucla, they split the hour and half difference between Adelaide of Perth, and set the clock 45 minutes ahead of Perth. Entering both South Australia and at Norseman WA, your car will be given the once over for fruit and vegetables, you cannot take them with you. I used to buy a bag of oranges to eat on the way east and it was either eat them or ditch them at the SA check point. It is not worth driving at night, there is too much out there to hit, roo's, emus, horses, cattle, etc, just east of Balladonia I once saw about 7-10 of camels 10 metres from the side of the road. Fuel is going to cost you, - no way around it, fill up where you can. Driving west in winter usually means you're driving into a head wind,so increased consumption. Roadhouse food is absolutely crappy, fried and reheated which is why I'd take fruit. If you can, freeze some water containers overnight to drink during the day. That you need a reliable car is a given, any tows or repairs will cost you heaps in both time and money. There is no phone service for most of the way or radio reception, take a USB stick or some CDs to play. You can sleep in your car, but its going to be a miserable night though its completely safe, I like hot showers, hot coffee and a sit down toilet in the mornings. For stops, there is an old Telegraph station near Eucla which is slowly being swallowed by the sand, at the point where you're closest to the edge of the continent, drive down the marked road to the car park at the Bunda Cliffs and you can see the coast line stretching away east and west, in front of you is the Southern Ocean with nothing between you and the Antarctic Ice, if lucky you may see some whales, you can, but I wouldn't, get over the fence and sit on the very edge. The Nullabor Plain is really only about 100km wide or so, the rest is really a table land whose name escapes me. The road is good, though I give way to the numerous roadtrains that use it. I used to do it in 4 nights and 5 days and I remember the GPS would be giving the location of the Balladonia Homestead instead of Balladonia Roadhouse, about a 50km difference. Traveling west to east, it would be Perth to Norseman or Balladonia Roadhouse/Motel, then Balladonia to Eucla, Eucla to Port Augusta, Port Augusta to Wilcannia, Wilcannia to Sydney. There are no tolls west of Sydney, set your cruise to 110kph and enjoy the trip. I'm envious and would love to do it again.

Two main options for camping: one, camp at a hostel/guesthouse/official campsite. You'll pay them a little bit of money, and they'll give you security and facilities like toilets and showers. Two, turn up in a village and ask the chief where you can pitch your tent. You can do this in most villages in Africa. Just be respectful. I have wild camped in the bush in Africa before, but generally feel more secure camping near a village. If you introduce yourself in the village, they'll assume your safety as their responsibility.

You'll absolutely need to bring your own gear. A thin mat (rather than a mattress!) should be fine, while a sleeping bag is rarely necessary; even when camping at altitude (in the mountains of Malawi, for example) I don't think I needed a sleeping bag.

The leg of your trip between Xpujil and Bacalar goes past Kohunlich and the complex at Dzibanche. Dzibanche is a regular ruin but it has a lone temple some three miles to the west, that from its summit, you can see Lake Bacalar and out to the ocean- it puts it all into perspective. I like the Dzibanche area because about every third farmstead is built on or beside a no name ruin. The area is heavily farmed so one can get a really good idea of just how densely the Maya inhabited the area before the conquest. All of the secondary roads going into these ruins are good, have drinks and snacks with you as there is nothing to buy as far as refreshment at ether ruin.
I've done the drive from Merida to Calakmul in 7 hours, going the coastal route, turning at Escarcega.
I've driven around Latin America with no one who spoke Spanish a number of times-with never much problem. Any problems have been over getting directions, your route has great signage, directions should not be a problem. My wife speaks Spanish like a native, we never have her talk at road blocks. Just hand them your paperwork, smile and you will be on your way. Tourism is a big money spinner in Yucatan, obey the traffic laws, watch out for pedestrians, slow moving vehicles, cattle in and along the road and the dreaded speed bumps. There are 50 million of them in Latin America, few marked. You will get the drill on speed bumps within ten minutes of renting your car.
I always buy a styrofoam cooler when traveling by car, I've even used a proper cooler as a suitcase flying down just to have a cooler big enough for my crew.
At Xpujil, the ruin Bacan is worth the effort. It sports some temples with the phoney steps, too steep for even a mountain goat and it has a moat. It is a compact site with some interesting features. The Hotel Calakmul in Xpujil is the best hotel and restaurant in town .
Bacalar is a nice area, there is a big sinkhole south of town that has been developed, restaurant, bar , a great place to swim.
You have a car, Majahual would be my choice over Tulum. It is Cancun, thirty years ago. There are lots of little hotels going down the south road out of town, you don't need reservations-just go.

I really don't recommend doing the Tour du Mont Blanc until at least the third week of June when the season officially opens. Before that, there will be a lot of snow making some sections dangerous or impassable. Re: a sleeping bag in mid-June, I'd recommend at least -10C to be safe. It can get quite cool at night and it's better to have one that's a bit warmer than you need than to be freezing each night.

That'll be great!! Thanks a lot bro...

One thing... can I find stuff to rent from Mastuj? Stuff like gas stove, tent, sleeping bag, etc.