[super vw]

Well for min work room around the cars... i would have to say 3 feet, i have about 3 feet to work around my project (shelving and benches take up lots of space) and its about the min i would want to work in, its fine if things get picked up and things stay un cluttered.. but once you get things all torn apart and clutter starts the build up, it cam become a little tight and a mess to walk/work around.

I think you should try and build it so you have around 5-6 feet around the car.
For work benches, make some ones that have a crapy(cheap top) and some that are nicer (like a lamanate or somthing) aswell as a 1/4 steel toped area for welding/ banging....ect. the cheap top ones make replacable so when they get all messed up you can easily replace it, this kind of top i like when making things, its great not to have to worry about messing up your counters whne the going gets tough...or whatever.

Cabinets should be large enough to store tall paint cans and other autochemicals and be strurdy and well ancored to the walls. get some beefy hinges to, dont skimp on hinges!
Make it so you have storage under your counter tops, maybe even some that have no shelf and only doors and no bottoms so you can slide a shop vac in witout having to lift it..ect

Dont forget a drill press, bench grinder, and maybe other large tools you use... at least i like to have all that as i like to make stuff, but im not sure what you do so...

MAYBE even make a "pit" under one of the bays if you dot get a lift, this would make under car work easy. i know a friend who did this to his concrete slab floor... it was a good 8 feet long.

Well thats all i can think of now,

Later,
Jonathan