what exactly is this, i know apexi makes them and they look cool, but does it actually improve performance? Based on my mods below would it help me gain significant power? Do i have to know alot to use it?

from what i've read and seen, it tends to add 8-10 hp to the wheels on our cars. granted, this is done by a professional who can dyno tune your car. i plan on having this done once i get my new o2 sensor.
later

All the S-AFC is, is a piggyback computer for your fuel system. All it does is modifies the air-flow signal to give you optimal Air/fuel ratio. Its not going to be somthing that you plug in and add horsepower. Yes it does look cool but witht hte list of your mods I wouldnt see you spending the 350 on it. You wouldnt really have a reason till you go turbo or nitrous to need to be adjusting fuel levels IMO.