Very little flight experience and solo adventure is fast approaching! Can someone talk me through the process?

you can get all the information about what should be in hand luggage and what should not from the Heathrow website. Make sure you get it right, especially regarding the liquids/gels/pastes thing.

take a large empty water bottle through security, fill from the tap on the other side. Dress for comfort in layers.

turn up in good time, go to check in with passport and tickets, drop off bags. Go through security (Takes ages). Head for departure lounge, wait. Board when called but no need to stand in the queue until it thins down.

repeat at stopovers. Find out when you need to collect your luggage - presumably at Sydney. If you have any queries or are lost, ask any airport staff; that's what they are there for.

(for ultra paranoia, have your passport, wallet and phone in your pockets, not your hand luggage during take off and landing. Then if what happens at Las Vegas happens, you won't be stuffed because you won't retrieve your hand luggage.)

Where possible use the same airline for connecting flights, if there are delays the airline will sort out the flight you have missed. With different airlines it's your problem.

For connecting flights keep checking the flight displays as you move around the airport of any changes.

Make a list of what you need to have with you such as passport, airline tickets, itinerary, credit cards, etc. Check the list before you leave home. I like to have these documents in a clear plastics folder so they are all in the same place.

Get to the airport with plenty of time so you aren't under time pressure to find things or sort things out if they go wrong. Allow plenty of time between connections. This is especially important at Sydney as the international terminal is some distance from the domestic terminal (there is a short bus ride between terminals). I would allow at least 3 hours between an international and domestic connection in Sydney.

Australia has particularly strict immigration and bio security checks so it can take a while to get through immigration and customs. Bio security imports (unprocessed food, seeds etc) are very strict so check the list of prohibited imports. There will be sniffer dogs looking for food etc.

Some people take a spare change of clothes and basic toiletries as hand luggage in case there hold luggage goes astray along the way (but note neverwinters comments above on limits on liquids, gels, sharp things etc you can take in the cabin).

Check your ticket which will have all the important things to do and times required for check in. For example for in Australia check in is cut off 30 minutes before the flight leaves.

In Sydney you'll have to collect your luggage and go through immigration and customs. Your flight will arrive at the international terminal. Flights from Sydney to Coffs Harbour leave from the domestic terminal - and separate building altogether. There are 3 airlines flying that route - Qantas Virgin and Tiger. If you are flying Qantas or one of its affiliates then they will transport you between terminals by shuttle bus. I don't know whether Virgin do this. Tiger definitely don't. Check with your airline to find out whether they will arrange your transfer. If not then you can get a shuttle bus outside the terminal (ask at the information desk) or get a taxi.

Beijing you should be able to transit without visa depending of course on length of stopover.

Virgin do have bus transfers between the international and domestic, so you should be OK, with the carrier you have. In Cofffs Harbour the walk aroiund Mutton Bird island is interesting, not sure how long you are in Coffs, but its easy to get to Sawtell, Bellingen. and Woolgoolga, and if you have someone who drives Korora Bay beach has lots of interesting coloured pebbles.

For transfer in Sydney between the international and domestic terminals there is a shuttle bus available for all passengers. QANTAS and Virgin seem to be offering something different as well -

http://www.sydneyairport.com.au/go/terminal-transfer.aspx

There is helpful info here but it starts to cover many options.
I suggest that you post which airlines your flights are with, and the depart and arrival times.
2 points
-,the empty water bottle is a good idea but it will likely then be confiscated at Beijing security check (even though you are just in transit)
- Australia's entry is not scary. Just answer the questions on the card honestly, and any quarantine matters will be simple and without any penalty.

Taking empty bottles isnt a problem because there are usually water outlets in the gate area. Empty bottles dont get confiscated.

Hi,
Agree with what others have said, except about taking things in your pockets. At most security checks at airports you have to empty your pockets, so it's better to have a bag to put things in( like a handbag). Some places ( like LA that I have just been through also make you take your shoes off, so slip on shoes are a good idea.
Some of the domestic flights like Sydney to a Coffs Harbour sometimes use relatively smaller planes which have smaller overhead lockers that don't fit big bags. If you have large non checked luggage you can use "premium Hand luggage" which means your hand luggage is tagged at the gate and then you leave it at the foot of the stairs going onto the plane ( that's right- might not use an aero bridge) and then you collect it there again when you get off.
Also, you definitely need to allow 90 minutes between arrival of international flight and departure of domestic flight at Sydney Airport. If you are booked with the same airline they will not permit you to book if the connection is shorter. I would highly recommend using the same airline if possible as it takes the stress out of the transfer and they will rebook your onward flight if for some reason your international flight is delayed. Remember that after such a long trip you will be very tired and not really functioning properly. Why are you going to Coff's Harbour? ( it's a nice place btw)