4 Month / Half Oz Trip - Advice requested

Sorry for the log post but my partner and I are planning for a 4 month trip around 1 half of Oz (up the centre and then either the west or east coast)

At this stage I am leaning towards a preference for the the western half.

We do not currently own a caravan or suitable towing vehicle. If we opt for the caravanning option both caravan and tow vehicle will be purchased 2nd hand solely for the trip (and a couple of weekend shakedown trips) and then sold afterwards. Caravan would be purchased with cash and the tow vehicle through finance (hoping for interest only loan options - but need to check with our Bank). Caravan & vehicle budgets at this stage are around $25k each (if I can get an interst only loan then vehicle budget could increase).

Planned departure date is early July and we are planning to stick to sealed roads between major destinations (eg if we do WA we won't be going down the Gibb River Rd) - ie no towing long distances down unsealed roads and we are not looking to typically camp off the beaten track

Also if we do WA I want to go into the Bungle Bungles but we could always hire a 4WD from Kununarra for a few days if need be.

My partner's father is a mechanic and her brother is a diesel mechanic - they have both strongly advised us against Landcruisers or Prados because they reckon they suffer too many mechanical problems when used specifically for towing (but I can't find any evidence on the net to back this up - exact opposite if anything). They are strongly pushing us to get the biggest \ heaviest vehicle we can afford for newbie caravanning safety (which makes sense). They reckon we should optimally look for a 3.0 litre TD Patrol (around '03 to '05) to give us off-road non towing options or alternatives like a BT-50. They even reckon a Territory is an option if we stick to the bitumen. My partner's biggest requirement for vehicle is comfort and she is sold on the Territory for both comfort and also that it falls inside our initial budget. Patrols seems to be mid 30's for the age range I mentioned.

In terms of the type of caravan my partner currently favours the Jayco Discovery Pop-Tops - the 16.52-2 model in particular which has an 18 foot body length. Other makes \ models are prefectly ok - its just that she like the layout of this model the most and we want a pop-top for easier towing.

There are a few items I am trying to figure out.

1) In this scenario do you guys believe purchasing a caravan and tow vehicle and then selling would be more economical then say using our normal touring car ('02 Holden Calais) and stopping in Caravan park cabins with a 2 man tent taken with us when we are in a pinch for accommodation?

2) What type of tow vehicle do you suggest? Can anyone with proper mechanical knowledge dispute the anti-Toyota stance?

3) Am I right in believing that with WA I can stay on sealed road getting between the major holiday parks?