Also set aside ~$50-$60 to take the car to a dyno and see what you make before all this stuff and then after. I have a feeling you will be disappointed, especially if you do just the intake manifold and no exhaust.
Think about this, air that goes in must go out. If you upgrade the air intake and intake manifold you are "basically" taking in more air, where does it go? Into your stock low flowing header, cat, and exhaust. Well that doesn't help does it.
The other thing to consider with the air in, air out concept is that you need to have the power to move the air. With the low HP of the b18b1 you aren't going to gain a lot by doing huge upgrades to without doing something to improve the power of the motor itself. Then you get into upgrading the cams, changing the compression ratio, etc.
Also, will the ECU know what to do with all this extra air in and out? Will it throw everything off and be putting too much fuel or timing in and effectively killing any gains you may have had?
A better question is, what is your ultimate goal (from what I've seen it's to have a "peppy" daily driver), and what is your budget?