Teams require stability, cohesion, feedback, retrospection and improvement.
Let the team form. Make it stable. Don't pull from or add to. Let it sit and gel.
Let it self regulate. Let it eject high maintenance high performers, lone wolves, and other forms of detractors. Empower it to self regulate.
Give the team a feedback loop and let it self improve. Measure performance towards what matters by the average of its members. Let the team use the data to find it's optimum size and resulting output for the task at hand.
Let it self reflect and evolve. Let is use the reflection to define continuous improvement and never short that investment.
The goal being not perpetual motion, but rather self generating accelerating velocity. Impossible for the individual to achieve, but doable, albeit extremely rare and difficult, for a group of individuals to achieve - a team.