Daylight not casting aspersions on the vast knowledge base on seabreeze and as someone who is currently doing the "Nomad" thing in a van (WA based) all I can suggest is visit a caravan based website like this one. They will be able to answer every question you have and chances are someone very near by may be able to help.

www.caravanersforum.com/

a word of warning. many caravans are well over their legal weight by the time you get on the road. my inlaws got a heads up on the police transport divn in WA checking nomad vans up north and put their van over a weigbridge. . after lots of stripping out of stuff they came to the realization that they had to get rid of their fridge,watertank and gas bottle in order to be legal.
THE van had been built overweight as the fitout had happened AFTER registration. . all thier traveling mates had the same problem. One was over 350kgs overweight
they traded in thier van for a new one and were really careful to check the paperwork etc. old van are having to be re certified by engineers to get back over the pits.
if your being offered a deal on a new/nearnew van start looking at the paperwork and even request it go over a weighbridge to confirm the weight.
you really need to do this before heading to WA this migration season

It might be worth considering hiring a van like the one you're thinking of buying when you get to that stage to try it out first before spending all that money, just to be sure.

I used these people a couple of years ago and they were excellent. Caravans are spotless and the Expanda one is within your budget.

www.allclasscaravanhire.com.au/

I reccomend renting one for a week and trying it out before buying your own. I did the same and towed to Augusta for a week of kiting. Was a lot of fun.

Also,.. be prepared for many caravan parks do not allow dogs. Some do provided it is on a leash, with person attached.

National parks do not allow dogs of any size, even if they are locked in the car.
There are signs up telling you to turn around if you have a dog on board.

Many of the outback stations don't allow dogs on the properties.
The ones that do say the dog will be shot if it's caught bothering stock.

Travelling with a dog really cramps the places you can go and not be treated like a lepper.

Thanks for all the suggestions, will go down the tey before buy and see what suits, so far the expanda is a must try.

My car is rated to 3500kg towing so hoping to have a good choice of vans

Looking forward to getting out there and giving it a try.