FJ40 with big tires on the highway will be a little scary and wander; however wheels very well in tight spaces. They don't carry much stuff either and get 12-16mpg highway. Leaf spring suspension and manual trans.
FJ60 with big tires will cruise on the highway nicely (longer wheelbase), carry 4 adults comfortably, can fit a twin sized air mattress in the rear for camping, can carry a ton of gear, gets the same crappy mileage. Leaf spring suspension and manual trans equates to a 4x4 ride quality but at your age you won't know any better ;p . They have power nothing (no pw, ps, pl or anything) carb'd 130hp/200ft/lb tq engine.
I'm 33 and love driving my FJ60. Going larger than 33" tires requires a gearing change (this is barely tolerable with the stock 3:70 gears). Gear change is going to cost $2K+ with lockers front/rear if not more.
FJ62 only came with automatic trans and had 4:10 gears and power everything. Keep in mind FJ40-FJ62 trucks are very rust prone in parts of the country that get lots of moisture/salt on the roads etc.
They have a little more HP/TQ and had EFI engine.
To do serious wheeling on any of the above setups you need to add a locker out back at the minimum and up front wouldn't hurt either.
FJ80- '91-92 has the same FJ62 EFI engine, different body style, more plush (leather or cloth), can seat 8 people, has power everything, automatic only trans, a bit heavier, won't carry as much as an FJ60/FJ62, and 4:10 gears, with body/paint that won't rust as easily.
FZJ80- '93-97 has a more powerful 220hp+/275ft/lb tq EFI engine, option for factory electronic lockers, auto trans and those are about the only differences vs. the previous year. These are obviously the most expensive of the bunch.
A nice thing about the 80 series trucks is that you could tow something if you wanted to, they seat a lot of people, power everything, sunroof, and plush leather. The factory lockers is pretty sweet as well.
Someone please correct me if I'm wrong on these points I tried to help him with.
Remember that these trucks need maintenance and things do break. So if you can afford to put in a lift with new tires/rims $2K or so (without labor), gears/lockers ($2K or so), HD bumpers $750+ for front, winch $750+.... then you will have a pretty bad ass wheeler.
In stock form though with 2.5" lift, 33" tires, a locker out back any of the above choices would wheel very very well aside from crazy rock climbing. Gas mileage isn't the strong point for these trucks. In town 10-12mpg. Hwy probably 13-16mpg depending upon speed, lift, gearing, driving style. They are not fast by any means either.
An FJ40 or FJ60 with V8 conversion IMO would be a sweet first truck and get the same if not better gas mileage (depending upon transmission/tire size).
Good luck!