A turbo timer is a good investment. Ive never used them because I drive my car to cool it down after a run but if you like to run it hard and shut it down it may be useful. A quality boost gauge is also a good idea. Gauges for water & oil temp EGT fuel pressure and A/F ratio can also really help. Stock gauges are usually pretty inaccurate.

I dont know if your car will have pre-cats but a downpipe and cat back exhaust is usually one of the first mods for any turbo car. Then pulleys some sort of engine management intake intercooler injectors etc. Usually the ignition system is one of the last mods for RX-7s because the stock system is more than good enough. You just want to make sure you avoid too much boost for the fuel available.

-j0lt