Unless your van is built to travel offroad, and you are a VERY experienced traveller, do yourself a favour, don't go that way. The van is 20 feet long. There's lots of room to take too much stuff. Having started travelling Oz in 1960, I strongly recommend that you park the van in your driveway, then live in it for about 10 days. Use the house for toilet and shower, only. In that 10 days, you will find out what you need, and what you don't need. So many "first timers", load up, only to realise that you probably don't/won't need all the extra gear. What are you going to tow with. The price of fuel can ruin the best of plans. Don't think for a moment that you have to have what everybody has, or recommends. The more gear you carry, the more fuel you will burn. The more money you will spend on getting there.
We have lived in our van for more than 18 months then bought a house. We have offloaded about 300Kgs of 'stuff' that I now KNOW I can live without. 18 months ago I didn't think I could. Next trip in a few weeks will be really travelling light!
The WA section is almost as good as bitumen (very wide and smooth and very little traffic) ,NT section a bit rougher but still a good road (similar to most outback gravel roads ) - travelled the Great Central 3 weeks ago not towing but would not hesitate to take our van across it if the occasion arose. Drive according to conditions and have a simpathetic feeling for your equipment. Running low tyre pressures DOES NOT REMOVE bumps or corrigations so slow down in these conditions.
GCR We were over it in June. It was Two wheel drive stuff all the way. Road was really excellent to the WA border. NT side was OK as well Grader had done 90 klm from Yulara toward Docker river, when we camped with him. I suppose the New Docker River Crossing is up and open by now. It was looking good when we crossed the river but still not open. Quite a few big Vans on the road when we were on it. Smooth as for about 1200 klm's
We came across a newly wrecked Trailer that looked like it was just a (new) Cheap Garden Rubbish to the tip, type of trailer. Been turned into a Camper with ally box and Tent built on it. Looked like the (far too light) Stud Flange on the Wheel Hub had broken off and the lot had rolled. On a beautiful straight stretch of well graded road. I would think speed was also a factor here.