Welcome mate! Especially you are from Melbourne.
BMWP exhaust is quite bang for buck if you want a bit of extra noise.
Like the others have said, handling mods will be most rewarding. And that is exactly what I have done. Get coilovers and LSD if like fun and go to track.
As for maintenance, depending on how many Ks the car has done, it is just mainly engine oil & filter, brakes and plugs. On top of that, you may want to do gearbox and diff oil. It is very easy to do it yourself on the 130i.
2012 BMW M135i | 8AT | Quaife LSD | ER catted DP | Solid rear subframe bushes | Bilstein B14 | M3 Front arms | H&R sway bars | BBK | Flash tuned | ER CP |