At our gym, our level 2 and 3 teams have 1 head coach and 2 or 3 assistant coaches per team. Our level 5 teams have 1 head coach and 3 assistants at all times.
we have 2 coaches with our teams of 20 or less and 2-3 coaches with 21 or more. This is good fo our teams as the coaches usually balance each other out.
At ACE, every team officially has two coaches per team. I'm not sure that is the real question here though. We always make sure there are plenty of coaches around when trying new stunts or pyramids. That's the critical time, I believe.
We always have 2 'official' coaches, but at various times during the routine creation, other coaches will come in and work with the team too to tweak things etc.