EZ-E, $3500 is high (but) real nice 1st gen's are getting hard to come by now. If the motor has 236000 mi on it without a rebuild - its going to need one. A 12a is good for maybe 100000 mi (if your lucky and take good care of it). Borrow, beg or steal a Mazda comrpession tester and check compression on both rotors (all 3 lobes checked with mazda's unit).
Big debate between the 12a and 13b motors, I like the 12a - street port it, open up the exhaust and intake, bolt on a couple webers and it'll run well. Earlier 4-port 13b's are desired also. These cars are light and well balanced. LOts of racing parts available too. Swap out the rearend (with drums) for a lsd with discs.
Mariah is a very good body kit, and expensive if you buy it new. Its my favorite. They also make a real nice 2nd gen RX7 kit for like $4500.
I'm now running a stock '84 GS with about 68000 orig miles. Paid $1800 for it last year. Had to put a new cat converter on (old one burned out), front brakes, one caliper, clutch slave and master cylinders. Interior is probably a 7 or 8 out of 10, exterior is silver and only has a couple thin spots in the paint (next years project).
Sold my '79 Fairlady last year and wish I'd kept it - I liked it better than the RX7. If I buy (find) another Fairlady in good condition, I'll keep this RX7 also - they are a nice car to drive, even longer distances.
Oh yeah, a small block also fits in real nice too !!
best of luck, let us know what you do.
Todd