Step 2: Selection of the Commander's Troops
First of all, let me get this drilled into your mind, the Commander should be a well known individual in your group, maybe a guy who knows strategy games, or a wingman's leader. Just make sure that the person can work under pressure. The defenders should, by default, have the advantage of numbers.
The Process: Just line up as if you are 1st graders picking teams for kickball, or, if you are feeling confident, go by voluntary response and let the troops pick their Commanders.