Your going in the right dirrection. Rx's love to breath so u do the little things first Exhaust (3" down pipe decat),Air fillter,8Psi max on std fuel system. That is about it if you dont want to spend much money.
If you do welcome to the World of the RX7, to get big Bhp you will need to buy Ecu (Haltech E6k),1600cc injectors+rail,fuel pump,Ignition Booster,T04 Turbo,Fmic then Street port it uprate the Stationry gears and u will have a car that will pulling 11's on the 1/4 depends on the boost level.
HEALTH WARNING. Rx7's are adictive and in the wrong hands deadly.Lol