If you want, come see me when you received your parts. I have built a few ICS based rifles and most part will fit with very little modifications.
You want to get the newer white Modify piston with the first tooth removed (I think they call it high speed).
A S100 will get you to about 340 fps if you have a VERY good airseal, but most probably around 320... rule of thumb is (M/S x 3.3)-20 = FPS will be a decent estimate...
Keep the stock hop-up chamber, but upgrade the rubber to a Guarder clear or Prometheus purple. It is possible to install an aftermarket metal chamber with some minor modifications, but the stock ICS chamber is way more efficient.
PM me if you want to drop-by... I am in Longueuil... if you are still in Brossard for now.
You should end with something similar to this, minus the G5:
