Can't comment on 2 or 3 because it's been so long since I went through, but in answer to your other questions.
1 - I've known several ex-rocks make good WSOps, so don't worry about that. As for your current trade being in demand, so is the WSOp branch! It's sad to say, but gaps in your trade are probably more acceptable than gaps in the WSOp branch, so you should still be OK.
4 - I do remember seeing something on Prune about airborne snipers, selected from regiment squadrons, maybe this is what you are referring to. I've never heard of non-WSOp door gunners otherwise.
HTH