I'm drunk right now but I see this post.
I tried to audit this but it's all good adviceThis really They are easy to run and maintain east or westI know its cool to have a shit car...but wouldnt at least some sort of 4WD be advisable? the "spirit" of this might get bored if you're broken down in the middle of a desert with only the love of your country to keep you warm.
ex-mil issue land rover would be the best to be honest, with a yak on the roof.
4WD is a two-edged sword. It gives you better ability to traverse rough terrain, at the cost of being heavier (worse fuel economy) less efficient (more moving parts = more friction = you guessed it, less fuel economy), and more of a bitch to fix in the field (more parts = more shit to break = less fue--*Ed: We apologize, this joke has been taken out back and shot).
[i]From what I'm aware very little of the trip involves cross country, but, if you take a ford fiesta you are fucked. Take a good wagon and know how to maintain it.
Seconding all the common sense suggestions like cannibalizing a donor car before you leave the UK. Also get a real mechanic. The most awkward shit imagineable will break down at the worst time possible, and you need someone who knows enough about cars to be able to know how to both jury-rig temporary solutions and make permanent fixes to anything that breaks.
You need someone common who knows a bit about all cars and engines and can fix you up in the eastern bloc.
On the survival side of things, bring water purification tablets in addition to a nice compact mechanical water filter. (Seriously, you're driving through a desert, water will be a primary concern.), a sheet of plastic for use as a dew collector wouldn't go amiss either.
DayZ may have taught you things but desert survival is fucking hard. Pack a few books and at least 5l of water extra per person per day, sling a jerry can in your boot and three days of rations per person for three days (hell, I fucking planned for that when I was in Newcastle with a bunch of six formers)
Get someone certified at least up to wilderness first responder, preferably wilderness EMT, before you leave. Better if you can cross-train at least two folks for it. Learn the specific dangerous wildlife along your route and how to avoid being poisoned/eaten/mauled by them.
Bring duplicates (or better, triplicates) of all your really critical survival gear. Maps, compasses, etc.
Deserts get fucking cold at night, bring good sleeping bags.
Get everyone on the team a good full-tang fixed-blade knife and make sure they know how to use it. Knives are useful tools to have. I'd personally find some weight/space for a hatchet too.
Get a -good- medical supply kit together. Not some namby-pamby gauze-and-iodine-and-aspirin kit, but a proper suture kit, antivenom for anything venomous along your route, disinfectants, cast-making materials, splints, a couple pints of blood plasma, buffered saline drip bag, etc.
Get a satphone. They're expensive, but being able to call for help is worth it.
Learn orienteering and navigation. Particularly learn to astronavigate. The stars make damn fine navigation tools. They're hard to lose. Learn to use them.
That's all that comes to mind right at the moment, but I know I'm forgetting tons of other advice.