The AP-93 is a single radio access point that is capable of 802.11 b/g/n OR a/n.
The maximum number of users supported is 255, however in a best practices designed wireless LAN there will be multiple APs in a given environment to provide coverage and capacity.
The number of users per AP comes down to how many you want sharing the bandwidth available at the end of the day. If you are comfortable with 20, 30, 40 devices sharing the available bandwidth (in the case of AP-93, that is up to 300Mbps OTA, typically yielding up to 150 Mbps once overheads are extracted) then the AP-93 will support any of these numbers.
I have seen even the older Aruba APs support well over a 100 clients at one time, on a single radio. That being said, each user is then 'lined up' to access the channel (since 802.11 is CSMA)...you don't want that long a line-up in most cases.