Hi SunShine..
Hope i can help..
Regarding your questions:
1. Australia is a very easy country to F&E. It's English speaking and has tourist booths around for assistance in booking of day trips and accomodations and directions seeking.. so no problem. Even better if you drive cos the roads are big and wide and Aussies are good and courteous drivers.. and the roads are properly signed. Just buy a lonely planet guide book or surf a lot to plan your route in general.. den after that, can work out details as you go along the way..
2. Sydney and Melbourne both have diff charms.. Melbourne more laid back, old town and nature kinda trips.. In melbourne city itself, you can see old architectures, trams and plenty of cafe.. Outskirts of Melbourne can do trips to Great Ocean road, or to mt Bulla and Philip Island (see penguins
)
Sydney is more a hip cosmopolitan town.. of cos you will see attractions like Harbour bridge and the world renowned opera house.. and of cos visit the nice beaches there.. shopping and more shopping.. but can oso do trips out to Blue mountains (i personally don like it) and Port Stephen and Hunter's Valley for some wine tasting and Hot Air Ballooning
If you wanna travel 2 places, you need to factor in the domestic airfare cost (can surf the few Aussie domestic airlines for good deals) I would suggest for honeymoon, don chiong to too many places and go see the nice sites in a v relax pace..
3. 4k for 2 people a bit tight for 2 places as honeymoon.. i suggest just go for one place and see the sites well.. enjoy the lazing around in a new city.. go explore the nooks and cranies of the craft markets etc..
I went on a shoestring to Aussie (Sydney, inclu blue mts, Melbourne Town, and Tasmania eastern coast) for 15 days and that cost us abt $1800 per pax inclusive airfare, accomodation and transport (we rented cars and took domestic airlines to the 3 places).. but mind you, it's quite on a shoestring.. eat mac, sometimes take bus, stay in hostel like and cabins.. (but fun though).. and our total cost was split 3 ways, so if you wanna live in better quarters etc.. 4K for 2 pax not v comfy..
Hope it helps