we have had a truck in South America for the last 3 years and for us this was the way to go as we were living in it full time. previous vehicle was a landy for asia.
most overlanders with toyota-landys type vehicles say to us that our truck is to big to get about in. but we went every where.
ours was 2.9m high which helped. most overland trucks are very tall and can stop you going into small villages due to low cables, so these trucks take a motorbike.
insurance was ony 150 pounds for us three years ago in the u.k but will be higher now. road tax was 195 pounds i think.
taking a vehicle into oz means cleaning-cleaning-cleaning,and shipping. have you thought of starting from oz and buying one there and doing the reverse trip
we averaged 18 ltrs per 100 km ( 7500kg truck) for the whole of our trip in South America and driving through Venezuela was a great bonus for cheap fuel, felt like being back in Iran.
we only drive at about 40 mph when travelling as we think you get to see more of the country you are in. we averaged 67 kms a day over our 3 years and will be looking to reduce this on our next trip
sometimes planning to much can take the fun out of it