like gen-x said, chassis are 99% of the time sound, but the body work is paper thin. ive just had my "92 welded up, rear seat belt mounts, some of the floor pan, behind the front seats and there were a few bulges in the front foot wells. i also had rusty sills, i had them patched up although there not structural on vits because they have a separate chassis. however if you find one thats really bad, i picked a tip up off one of the norfolk rhinos club member, he said knock some scaffold tube down the sills and then weld them in: rock sliders! my first vit also had problems with the rear wheel arches, they were virtually non existent when i got the car, also the front wheel arches can also go. i think its generally a case of peel back the carpets to see whats lurking below them. oh yeah, and if the body is really rusted, bear in mind what everything else metal might be like, brake pipes for example.
as for 8v and 16v
the 8v comes in either a carb model or a single point injection, whereas the 16v just comes in multi point injection (i think). the 16v might have a bit better acceleration because of the multipoint injection, but to be honest there probably wont be much different between the two. the 8v might also have better low range torque, and the 16v better mid range, but again there probably not much difference.
also, like gen-x said, drop dave jones a line at bits4vits, personally im going for lifted springs rather than spacers. ive read gv springs can give a good lift if not procomp do 1"1/2 springs. as for tyres, popular choises are colway mt's and greenway machos, but im sure other people will add there favorites.