hey and welcome to torquecars mate.
best starting point is if forced induction start with a basic remap, preferable one that can be custom altered a future date to incorporate other mods
for NASP cars, start with breathing. Panel filter or induction kit, exhaust - go for a whole system rather than just back box. then power boost valve ( fuel pressure regulator ) cams, porting larger injectors and fuel pump
more extremes gas flowing the head ( can be expensive on some cars ) fitting high compression pistons and conrods or forced induction