If you're looking to just sit and dps, go SS. But no matter what spec you go, you have to reset dampers and use instant charged burst every 6 secs if possible. Slinger/sniper is all about positioning, and awareness. The ability to kite for space helps a lot to.
As for stats its all personal choice, no accuracy or 105% (you canget something like 104.w/e with 2 enhancements and comp bonus). For crit I go around 35%, alacrity 6-7%, rest power. I switch my stats around a lot, depending on spec, 4s, solo, reg, or reg premade. But this is a decent general outline.
Rotation, is vital shot, charged burstx2, trick shot, aimed shot, trick shot, pen rounds, trick shot. Always keep vital shot on target at 30% or above if possible. Below 30% not worth it, just execute, and trick shot.
Haven't played tor in over 2 mos, so I am have used the wrong skill names. But again sniper/slinger is all about awareness and position. Also use crouch, never use roll into cover, see so many people use it