Firstly welcome to the forum :)
I guess coming from Australia you are looking to escape your hot summer weather but do be aware it will be cold here,possibly you'll see some rain and in Cappadocia particularly highly likely to see at least some snow.So for clothing think warm layers that you can peel on and off topped off with a warm waterproof coat,a hat,scarve and gloves-and bring lot's of socks with you!
I don't know when you last visited Istanbul but the city changes and improves all the time so there could well be things that you haven't seen since your last visit.So ideally allow 5 full days for this huge city.
Selçuk Ephesus makes a good base for visiting other places too so maybe allow 3-4 days there.You could go to Şirince, Pamukkale,Izmir,Bergama(on a longish but doable day) and Aphrodisias.Thankfully this is where you are likely to see the best of the weather.Although it rains it seldom gets snow.
Cappadocia...one of the great joys here is walking in the many valleys but it will depend on the weather how much you can do.If deep winter comes early some valleys may be blocked but there is no telling what the weather could do,it could be a mild winter in which case you may not see any snow,or only a sprinkling.But I would think 3 full,well planned days should be enough in winter.
So Ist.5 + Selçuk 4 + Capp. 3 =12 so maybe you could increase Istanbul a day to allow you to take a day trip maybe to Bursa for example.And you could add an extra day to Cappadocia to include a visit to Konya .this depends on your interests,youll know best.
In winter time flying is the better option especially if the roads are bad with snow.All of these are long overnight journies by bus plus,whilst our domestic airlines are always very economical, in winter time they are even more so.You could well find that flights work out cheaper than the bus in many cases :)
Istanbul to Cappadocia 10 hours by bus,80 minutes by air.Istanbul to Izmir 9 hours by bus ,60 minutes by air.Cappadocia to Izmir 12 hours by bus 90 minutes by air.No comparison really is there?BTW,on this route there are no trains that would benefit you particularly.If you like train rides then we can slot some in but you'd be no better off either time or money-wise.
As you'll know Istanbul is served by 2 airports and the cheapest and most frequent flights go from SAW on the Asian side.Cappadocia too is served by two airports-Nevşehir and Kayseri and again the latter has the cheapest and most frequent flights.Turkish Airlines,Anadolujet,Pegasus and AtlasGlobal cover the route
There are direct flights between Kayseri and Izmir but these are not daily so you would need to see how flights work out against your travel dates.Pegasus and Sun Express cover the route.
Flights between Istanbul and Izmir and virtually hourly with all the above carriers plus Borajet too so you have plenty of choice there.
Just a thought;if you decide to include Pamukkale -and also visit Laodecia too when there to make a proper mini trip ,then you could fly back to Istanbul from nearby Denizli airport.Flights from there go into both Istanbul's airports and are with Pegaus,Turkish Airlines and AtlasGlobal.And if you do go to Pamukkale then the ride from Selçuk can be by bus or train,both very cheap.
For transfers to and from airports you'll have a choice of public transport,transfer companies like Havataş and Havaş and also private transfer companies who run shared shuttle buses (particularly in Cappadocia and Pamukkale)these typically cost around 20T.L per person ,are door to door and reliable.
You'll be able to find apartments in all the places you intend to visit and Airbnb.com is well represented all over Turkey nowadays plus of course booking like Booking.com,Agoda etc.,and at that time of year you should be able to find very cheap accomodation,even more so this year as tourism has been so quiet.
I would suggest that upon arrival you try to move on to your first destination immediately and save huge Istanbul to the end.I know you'll be pretty D.O.A :) after a long haul flight but you know what Istanbul is like and so will know it isn't the ideal spot to recover from jetlag,much better to do that some where quieter such as a Cappadocia village or peaceful Selçuk.Of course this will dpened on your arrival time and what suitable flights are available but defo worth considering.Those who've done this are always pleased they did.
So now you can start checking out domestic flights to see what prices are like and how they fit your budget.Do check the airlines' own web sites for best prices and most up to date schedules though.Hope all this is a help to you!
