there's a few ECU's you can get Apexi, greddy e-manage, hks to name a few
some are easier to fit than others, some a straight swap others you need the looms and someone who knows what there doin
as for "getting modding" there's so much you can do, if you gonna be N/A modding like myself you wanna get the car to breath more easily, so air in exhaust out a few things you can do
induction kit or performance filter
new back box
de-cat
manifold
port and polish the head
camcon
aftermarket ecu
throttle bodies maybe
final drive kit
light weight flywheel
uprated clutch
you could go for a supercharger or turbocharger, think you can run about 0.6 bar boost then your need injector upgrades new fuel pump and other bits so you better be prepared to get your cash out
if you wanna run 1bar boost your need to uprate your internals so you don't blow the car up
some mods will depend on what your set up is like, cams and pulleys ect
how much do you wanna spend ????