It depends upon your requirements but below are some best practices.
Keep the number of SSIDs less as as per the requirement. Running too many SSIDs will consume more airtime.
Power up AP with POE+ (802.3at) so that AP can function with it's full power and capabilities.
If number of clients connecting to this AP are too many, prefer using 2.5G port, to connect R750 with switch, so that it can get good backhaul with wired network.
If you have a router or firewall already at site, avoid using Unleashed in Gateway mode.
Since you have just one AP, 802.11r is not required so do not enable it in WLAN settings.
If this is the only WiFi system in the area, you can utilize 2.4G radio in 40MHz channels for better speed. However, make sure area is not polluted with other 2.4G devices, else interference will increase and you may face connection/performance issues.
Make sure you place the AP in a place where it can cover maximum area. May be do a site survey for perfect placement. There are many 3rd party applications available for a basic site survey.