I run with a 3 hunter setup for a change of pace and I really enjoy it. It's not too bad if things get into melee, you have your traps and your disengage to fall back on

I'd suggest sticking with PvP and questing content though. They're really fun to stand in AV at IWB or SHB and rip apart the horde as they run past If you were doing 5 hunters, I'd suggest steering clear of 10 man BGs. You get a LOT of hate if things go wrong

As far as heroics and instances, as I only run 3 I can't comment but I agree with the comments posted above.