Starting with 4 trolls gives you a wall of strength unmatched by most teams, however comes with quite a few rolls you'll need to make keeping them in the game. For this reason I'd recommend starting with 3 re-rolls, as the trolls do NOT have loner, so may use them freely. 5 goblins seems to be a working amount, granting higher strength and a screening ability than the snotlings, who in turn are able to use swarming and move to either accompany trolls, or handle the ball for your team.