Hmm, this seems perfect for E6.
Everyone starts at level 1, but gets XP and cash for each kill (normal), assist(if you injure but don't deal the killing blow), defense (killing or assisting within the "home base" gives bonus XP and cash), and flag capture (This should give team resources, too). They can level and buy between games. Everyone should auto-level to be at most one level behind the highest level guy, or else it will be a downward spiral once you start falling behind. Once everyone is level 6 they only get cash and XP
Map sizes should grow as people level to allow for the increased options. On small maps you respawn within the home base after two rounds, on bigger maps its also no problem to respawn after one round, because just moving back to the action will take a while.
Obviously some things may need to be restricted, such as:
-You can't teleport into or out of home bases (and anyway teleport as a spell won't be available)
-You can't teleport with the flag
-I would say no summoning or calling, but that's a matter of taste, I guess. Summons obviously slow down the game
-Consumables have a limited allotment each game, OR could perhaps even be quick-bought within the game (for instance as a full-round action)
-The usual others that don't make a sensible game, such as infinite loops of any kind, etc.