seriously; feed with tongs, try to only let the siphon in for vacuuming, in general minimize the time that your hands are in the tank.
if he does sting you is not fatal unless you're allergic, otherwise it just really suxxx.
yes they can, and it's a good choice too, so are marine bettas and sweetlips.
(the sweetlips i think MIGHT get too big, have to refresh myself with adult size)
First get the tank. Do you want sand or crushed coral? I would use 4spotted groupers to cycle the 240. They don't get large and can handle brackish water.