It would fetch you a good amount back if you do sell. Plus its kind of a waste if you don't need all that power in the first place. Good luck.
Not on a case that takes an atx psu. You'll def need the bracket
Also, I contacted Corsair about replacement cables for the SF600 that are longer in length. They didn't have an ETA on them but they will offer individually sleeved type 4 cables sometime soon. The RMi and SF series use type4. Reduces ripple and provides more stable power to 3v, 5v, and 12v rails.