When I setup in my garage, it is approximately 320 sqft. I've had up to 8 people training at one time without any problems. It takes great discipline to be aware of where your neighbors are. I've also trained in space approximately 220 sgft with 6 people.
My current space is 704 sqft and I've had up to 35 people training. Again, discipline is the order of the day. And yes, we do take ukemi. Mat space management is alway a fun challenge.