Hello, I just got my 1st Nissan and it's a 300zx TTop NA 2+0 for 500$. So far I have changed the heater core hoses, dual electric fans with relays,battery relocation to hatch, silicone radiator hoses and PTU relocation to under nose panel. I just ordered CXracing cat back exhaust 2.5 and a set of headers, with an egr delete kit, plus a 90°flip up steering wheel kit also a lower kit. I like the car as it's a real head turner. Any ideas and advice will be helpful and thanks

Welcome!
As a $500 '90 NA, I'm going to advise you to check out the fsm in the "everything you need to know...Z32" sticky, it will help you out immensely as you sort out the myriad of issues a 1990 will have with the injectors, connectors, and elsewhere due to the old style injectors/connectors and the age of the car...unless the PO serviced all of this which on a $500 car seems unrealistic.
Personally I would be focused on getting all of the expensive and difficult services done before modding the car, since it's such a consistent and necessary need for these cars and especially the 1990-1993 models, bet hey- it's yours and you do as you like.

Thanks for the insight cause I plan on upgrading the injector harness and doing a LS coil pack swap. Timing belt and water pump will be done by Christmas.