I've done a very short sprint tri in a pool. In that one we started in the water but could push off the walls. Flip turns were allowed. Two people shared a lane by doing circle swim (always on the right side of the lane) and there was a volunteer that counted laps for you and put a number in the water for you to see on the last couple of laps.

I've also seen serpentine tris.

I'll be interested to hear how yours is going to be run.