You won't see much gains until you work on the internals. But of course, you won't see much gains with the internals until you have worked on the basic external bolt ons, i.e. exhaust and intake. After you work on those, do the underdrive crank pulley, the assessory pulleys(over-drive)Pulleys, cam gear, fuel rail, larger injectors, fuel pressure regulator, ignitions system(MSD SCI), Fields or Apexi AFC. Once you get all of that stuff, move into the internals. Of course you will need to port and polish the head, do a good job on matching the ports for the intake and the exhaust as this will free up some power! This will then take full advantage of what you just modified on the outside! Crowler makes an awesome cam shaft that has more of an agressive lobe than the OEM. This alone will gaurantee you 15HP/torque because of that

. You can also get a higher compression into you combustion chamber by using a thinner copper head gasket. Do this only if you do not intend on force-inducting it anytime soon. As you will want to lower the compression if you do that!! You will gaurantee yourself some gains with that, but you need to balance out the A/F and timing or you will be detonating, and THAT IS BAD!

With the cam shaft in place you are going to need Titanium retainer/springs or your risking floating springs and this is also bad! VERY BAD! You can kiss your valves goodby! :o Then there is the block. The only thing you can do to the block is sleeve it and blueprint it! As that is very expensive and you might as well have bought a B16 or B18 if you do this! THe sleeving is for the forced-induction and preventing the cylinder walls from vibrating and destoying themselves as well as the bottom end. You can also get the crank lightened, but then you are going into a delecate area! The transmission should not be ignored as this is the thing that contacts the wheels to the engine! You have to upgrade the clutch. Your OEM clutch is made to withstand moderate drivers and it is built to withstand low pressures. A stage 2 in any application is recommended if you are street driving and take the car to the grocery store a lot. Stage 3 clutches are intense and require you to pay attention all the time or you will be stalling or hitting the person in front of you at a stop. Kinda like you forget your car is in gear when you start it and you realease the clutch, then it jerks and jumps away from you. YEAH, That way!

A lightened flywheel will release a lot of rotational mass and turn it into POWER! YES, you need this too! You might as well if you have the tranny apart already, right?
I strongly suggest you take your time and get the right parts the first time. Cheap parts/deals will only hurt you in the long run and won't prove to be much of a deal! Stick with brands that you know and can trust. But all in all, OEM is the most dependable of all parts.

Hope this helps!