First off, I love your car. I had a black 90 GXL. The black FCs are so bloody rare, specially a S5
Do exhaust headers first if you going to mod. The header is ultra restrictive and while you at it, converted to a single high flow cat...if you want to stay green, if not, just take them off. check out this forum, slcrotary.com, small community, but smart people and great forum. Don't run higher octane than 87 or 85 if you are in high altitude. NA FC dont like high octane unless you got the timing set for it. all you will do is lose gas milage and power. Dont run synthetic, unless you dont have cats. And do Rev it out from time to time, so you dont get carbon build up and pop an apex seal. Just some useful tips if you didnt already know.

If you going turbo rotary with stock NA drivetrain, dont go over 250whp. but if you do a regular piston motor swap, the drivetrain is good for 500whp.

If you do a turbo, Dont worry about the high comp rotors, just make sure you got fuel management. My friend is making about 230-250 whp in his S5 NA with 7-8 psi.

If you go T2, then you need to swap everything out from motor to rearend.