OO ok, well first off, the AFC's are piggy-back systems that hook up to your stock ECU(comp.) and it is really helpful for getting the car to drive muchh, much smoother, and they allow you to play around with the air-fuel mixtures because as of stock.. the cars run really, really rich which is why, as everyone has said on threads, that if you mash your gas you dont really get that power for a few sec, until your rmps catch up with your fuel being dumped into it..(roughly), they are great because once you lean out some of that fuel, you can get the immediate power boost when stepping on the gas if you tune it right (aka, with wideband.. should get one, they are worth it by far)
-BPV is what you have in there stock, its basically the same things as a BOV, but the BOV's usually vent to the atmosphere, unless you recirculate them, they both vent off the air that is pushed back into the turbo when your throttle-body closes (the plate that lets in air when you accelerate.. very general description, connects to the cold-pipe incase you didn't know like i had for a lil bit lol)
and if this air isn't vented it pushes air back into the spinning turbo which screws it up over time, so, if you look at
http://www.mazdas247.com/forum/showthread.php?t=40956 you can find all you need to know about that, i suggest reading it, if not all of it, great info.
Other than that, i haven't heard of an HKS exhaust, but im sure they are pretty good, turbo-back is always good as far as more power.. um, ya get the corksport hangers with them as said b4.. andd that's about it! The more you read about stuff the easier it becomes.. might take a while to get through some info, but its cool to know that you actually learn a lot with all this info, and how it makes so much more sense lol-gl
-also i noticed that b4 when you said that they are 170hp and dynoed at 150ish.. the 150ish is the whp, so its still 170hp, unless they did it at the flywheel which i dono who actually does that.. but ya just fyi i guess