Re: Coaches to class ratio.
1:7 or 8 is optimal when teaching skills...
If the class is all relative advanced or there is little skill work involved 150 burpees for time e.g. Then it's all about can you be bigger than the room in which case you can coach quite a few people at the same time.
It gets tough with mixed levels of athlete at greater than around 1:10 IMO. Especially if you are constrained to a one hour class. But we've coped with 1:20(ish) when necessary...it happens if you don't limit class size, or get a random rugby team group that decides to drop-in.
Open gym should have someone staffed and really should be someone who is CPR qual'd (you never know!) and even though they may not really be able to save someone, at least you are covering your butt.