Please don't take offense, but if you don't understand the meaning of FET and opamp, aren't you biting off a bit too much?
There are plenty of good commercial units out there. You don't also built your car from the ground up, do you?
Personally, I'd go with a decent Fishman setup. Most standard acoustic electrics will have at least three bands of tone, many have four. If you still think you need a parametric, take a hard look at your amp and speakers to see if they aren't the real problem. If not, throw a parametric in the effects loop (or in line with recording, if that's the issue).
If you are looking for parametric because of feedback, some preamps have a built in notch filter (or you can get a feedback eliminator).