Game length is really just preference. Nobody wants to spend 30 or 40 minutes playing one battle, but if they are too short, then you really won't find satisfaction in beating the opponent.
Something in the middle is best. If there is an option to set the number of villages on each side, the match length could be altered depending on how much time you have.
Yeah, I expect it'll take a whole lot of combinations to that work. Villages, weapon power.. ect.
And there's also the fact that some players aren't experienced, so it won't work perfectly. You can't win 'em all, kid.