A single AP-105 would support 50 users easily, however in an auditorium/theatre design there are typically more than 1 AP with any best practices deployment. I have seen up to 230 users on some of our APs as an example.
If I had the design in front of me and was asked for a recommendation I would do the following:
- place two dual-radio AP-105s into the environment
- ideally home them back to two different LAN switches.
- activate spectrum load balancing, airtime fairness, band steering, and probe response threshold
This approach maximizes capacity, high availability, load balancing purposes.
A single AP-105 could handle 50 users, but remember 802.11 is a CSMA half duplex protocol. You want to minimize users 'waiting in line' to access the channel... how do you do that? Provide more channels is one approach (two AP-105s provide 4 channels for users to connect to)
All this ensures that the experience of all your users is optimized and readily available under all conditions (normal and abnormal, busy hour, and steady state etc)