I rather like the woman in the background looking on. When I spotted her, I chuckled and got the impression that she's thinking, "Ugh. Men!
I think the amount of characters you have is plenty. Any more and it might become overkill and a little too unrealistic. That's not to say twenty bar hoppers won't gang up on two men, but with the expressions on the main character's faces, I'd say this is a bit of a game for them. More brawlers and I would think they'd twist their faces with man-rage.
For little things, what about popping up the cowboy hat on Thomas a little so that it doesn't look so stuck to his head. Even a movement like that could send it tipping back just a bit; not enough to make it fly off, but enough to expose some hair. Also, the guitar looks a little out of place only because it's hard to discern its point of origin and appears to be broken at the neck. Is Alex flinging it back? To me it almost looks like he's mid rush forward, and if he was tossing it, the angle of projection seems as though it'd hit Mr. Blue Plaid. (Don't ask for specifics. I haven't done that type of math since high school!
) But I hope what I said makes sense! If he was aiming for Guitar Face, you could always turn Alex into the turn, with both hands on the guitar for force.
Otherwise, a very lively piece!