Biggest question not asked: Is the car the engine/trans/rear end is going into a S5 (89-91) or S4 (86-88). If S4, you're in for a lot of work as the wiring harnesses are not the same and incompatible. Also, what is your plan for engine control? The stock ECU will not be able to support 250+ whp. At the very least you will need larger injectors, a fuel cut defender (if keeping the stock ECU), and something to modify fuel timing (Rtek is the easiest).
There's not much rotary support here. Check RX7Club for the most history but there's a also lot of technical information and experience on RotaryCarClub and NoPistons.