The best advice I can give you is to go for the newst Corvette you can afford, though, stay away from the '97's. I've heard a lot of stories about '97's that had major electrical problems.
For C4's, I know I'm biased, but the '96 is a great year for C4's. The last 3-4 years of the C4's where great all around. If you can find a ZR-1 you like, jump! Just ask Rob and JT what it's like to have a ZR-1. I doubt you would ever regret buying one of those monsters.
Other than buy the newest 'Vette you can afford (minus the '97's) and all the regular used car stuff like an inspection, maintenence records, stuff like that... I really dont have much to offer (on this subject)
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
I have never owned a C4 but I would like a '96 Collecters Edition with the LT4 and 6-speed. Chevrolet refines the Corvette every year so it would seem that the '96 would be the most refined of all C4s. I saw a black '99 hardtop locally for sale a couple weeks ago for 33k. Looked like a real nice 6-speed car. Also you can find ZR1s from the first couple years at fair prices if you want a more exotic ride.