the short answer
Hire an assistant coach when you are at roughly 80% of your coaching capacity - a waitlist, slipping check-in quality, and no real time off - not when you are already maxed out. First confirm the bottleneck is coaching, not admin: if it is admin, a VA is cheaper and faster. And confirm you are not simply underpriced, because raising prices often beats adding a coach. Systemize what you do before you hand it over.