Welcome to the fun...
In general buying an older Corvette is really no different than buying any older car. Note, in general...
You know you should check for rust on all metal parts, check the condition of all the rubber parts, make sure everything mechanical is in working order, are there any body repairs, how does it drive, any smoking parts, any fluid leaks, any strange noises, etc...
There are some specific issues related to Corvettes. The easiest and probably the best way to help you with these is for you to scan through the various topics / posts on this forum.
I can't say enough good things about the people and information on this forum. You get to be part of real people's experiences and can get help from friendly people that have actually been there and done that.
Again, welcome... and have fun (that's what this is all about...)
P.S. You mentioned you were going to look at a 76. When you get back do a post on what you saw and any concerns that came up. Good luck and let us know what you found...