1. Depends on which SLG you have. Is it the UL, or the basic? I believe that they can each take different grips.
2. Yes, the SLG uses Autococker threads.
3. Best hopper is up to the player. I dont find the SLG to be a particularly fast gun (reliably) so I would not bother paying attention to the BPS of a loader, and I would set the speed of the hopper to around 16-20 BPS to avoid having too much pressure on the ball stack. I love my Pinokio, but it is a bit large. However, a Rotor, Prophecy, etc will be just fine. Get an electronic hopper, and you are pretty much good to go.