Hey mate. The best bang for buck mod would be turbo charging your car. But to appreciate the power you should initially do those small mods to mentioned. But don't do them all at once...you'll learn to appreciate each part more this way.

I would mod in this order:

1. Intake
2. Catback exhaust
3. Headers (if you don't think you'll turbo charge down the track, also good if you decide to supercharge)
4. RBC intake manifold
5. Forced induction.

Atleast this way you will be more prepared for the power...but keep in mind you may also need to upgrade your brakes and clutch.

That covers the basic performance mods.

Don't forget you also need handling mods, ie suspension, sway bars, wheels and tyres.