Aside from the crank issue, the motor is fucking indestructible. Biggest rust area on mine is in front of the rear wheel well on each side, but it's been through quite a few winters.
For pretty good deals on used parts, I usually go to http://www.planet-miata.com . It's a Miata only junkyard in PA so the parts usually ship quick. Just make sure you double check that they have the right part number down that you want, they do all ordering over the phone and I've had some issues before. Nothing that they haven't made right though.
If you've got any specific questions send me a PM. If I don't know I can probably find out. Definitely check out http://www.miata.net and the forum there, it's a bunch of old people who don't have a sense of humor but there is a shitload of information there, especially in the "garage" section.