Another thing to keep in mind is trial runs. Once you have decided what setup you're going for (RTT, awnings, how many spare wheels/tyres, amount of fuel/water you'll carry, etc), make sure you do a few shake-down trips with the vehicle loaded to, as near as possible, your final travelling weight. Looking at your planned trip itinerary, try to mimic, as much as you can, some of the terrain and climate situations you will be travelling through. Much easier to address problems without the pressure of deadlines for ferries, visas, carne's etc.

Use these runs to work out tyre pressures for bitumen/sand/gravel surfaces, (check temps and pressure changes). They will also allow you to find the "sweet spot" in road speed, where the vehicle seems to be happiest. This will help with your ultimate trip planning.

The runs will also bring to light any weeping, leaking or noises resulting from the work you have done in the meantime.

Weight distribution can make major differences, too. A friend found an amazing amount of difference in driveability of his vehicle, just by moving the RTT backwards or forwards a foot or so. A badly balanced vehicle can mean the difference between feeling good at the end of a days travel, or feeling like you've been dragged backwards through a cactus patch!

Mildly jealous of the trip you have planned, and the vehicle you're going to do it in!