Parts-wise there are some suppliers out there. There are two biggies:
(These people have lots of my money. They're very nice and helpful and friendly if you call them up on the phone to ask newbie questions as well.)
(Also very reputable and pretty good on the phone.)
Depending on what state you're in, there might be better/closer suppliers. If you head over to www.alfabb.com
there is a pinned list of parts suppliers.
Generally mechanical parts are easier to find than trim (or body) pieces, so try to find the cleanest, most complete example possible.
Rust is an issue with any older car, despite the fact that every seller will tell you theirs is a "California car that has never seen rain/snow/salt." If you're buying a car to drive, try to find a good one. If you are buying a car to restore, you can afford to find a few bad spots (although all said and done, mine wasn't too bad, except for the door sills/rocker panels, but you pretty much have to expect that those will be bad.)
I think markvrs misread your post. The GTV/Spider buyers' guide is for cars we never got on our side of the pond, and I'm sure you mean auto as in automobile rather than automatic transmission. BTW the gearboxes can be a bit of an issue. You want to find the smoothest one possible. Some gear (normally 2nd) can be a bit crunchy. Again, if you're looking to buy a model and drive it away with no work look for smooth changes. If you're buying a car to rebuild and fix, then a rougher synchro may not be an issue for you.
On AO the Classics Lounge is where we discuss the old stuff, but the traffic down there is pretty light, especially compared to that other forum I mentioned above. Still, we try to help when we can. You might find it helpful to dig around there and see what we've discussed in the past.
I'm not as up on the American market as I am on the Canadian one, but I'd guess $6,000 is a bit on the low side for a really good, clean, driver. I would guess a car at that price would need a bit of work and show some wear and tear, but then again, you might just have found somebody who wants to sell quickly.