The melee-only, spell-only and commune-only categories: do those refer to groups of classes, or just what skills can be used during combat?

Can a contestant enter in more than one category? For instance, in the open section as well as the commune only?

If so, that's going to be a huge number of matches. I would expect most people to enter in every section they qualify for.

If you wanted to narrow it down, you could optionally get rid of the open category and make it so you have to win your "class category" in order to advance to the "world series" tournament.

Have the three class-tournament winners do a 3-match round-robin. If two of them win both matches, have those two fight to break the tie. If all three tie then...uh...call them all co-winners I guess.

Optionally, if one of the class-tourney championship matches is especially close, you could give the loser a "wildcard" invite to the final tourney, to make it an even four. Then, instead of round-robin, do a normal single elimination.