you'll totally be able to do heroic/regular trash with a 5 hunter team and grind rep, but if you add a tank and a healer to the mix you could also do bosses. A number (a majority?) of regular bosses will be doable with a 5 hunter team, a minority (1-2?) heroic bosses would be doable.

You could also take 3 hunters and find a tank/healer and do most heroics I'd imagine.