I’ve worked on a large hotspot project some time ago and I used RB411AR enclosed in Cyberbajt sector-box antennas.
If I was supposed to do it today, I’d use Groove or Metal and omni antennas or compact sectors.
Instead of an “old” RB411AR i would suggest the new RB922UAGS-5HPacD if 2.4GHz is not needed for legacy devices without 5GHz support.
The new 802.11AC should better fit to the up to 30 people on ONE SINGLE access point. Because WiFi is a shared medium the users would benefit from different streams in AC instead of single transmissions that will be paused on every other transmission in 802.11g (which is rather lame today).
The other thing is the more of CPU and RAM on the RB922 which will fasten transmissions.