This could have been posted within the performance section.
However, the first thing that I would do is distinguish what type of performance you want from your vehicle.
You can build your self a $10 000 motor that won't perform anywhere under 3500-4000RPM, or you can spend $2500 and have it quick enough from lights to lights.
Overall, you are attempting to improve your volumetric efficiency.
Volumetric efficiency = percentage of your total swept volume that is actually utilised.
First thing that I would do is to build a decent intake system, then have your cylinder head modified to compliment all of your current mods and will also make full use of your future modifications.
However, you will begin to minimise your reliability.
But on the positive side of things, your ECU will be able to compensate for a large majority of your naturally aspirated modifications with out too much hassle.
Mind you all of your NA modifications will need to be carried out properly, no backyard jobbies unless you are confident in what you are doing.
Do a bit of your own research first, a good place to start would be with your local engine reconditioners, they should have the information you need to carry out what modifications that will satisfy what gains you are after.