Yes, I think adding a minimum troop number is a good idea. There should be a minimum number and a maximum troop number the the players can set before the match. Or choose to leave one or both blank, giving it a random nature.
On the note of randomness, there should also be an option for the troop types to be randomized. This would create some advantages and disadvantages in the battle leading players to have to improvise with placement, movement, and terrain tactics.