R1D2 wrote

As you wrote, the CPE510 supports 802.11a/n (5 GHz standards), not 802.11b/g/n (2.4 Ghz standards). To support 2.4 GHz you should consider use of a CPE210. For a PtMP setup with as much as 9 CPEs you should be aware that their antenna beamwidth is 65° (CPE210) resp. 45° (CPE510). Depending where the client APs are located, a WBS210/510 with a sector antenna such as the TL-ANT2415MS resp. TL-ANT5819MS would probably the better choice for the serving AP (both antennas have 120° beamwidth).

What also needs to be considered before buying the devices is the distance of the CPEs to each other. Having 9 devices in an area of 50-80 meters distance from the central AP will most likely cause interferences in the 2.4 GHz frequency band. Since in this band you have only 3 non-overlapping channels in 802.11b mode (4 non-overlapping channels in 802.11g/n mode and 20MHz channel width), a setup of 9 devices will require careful configuration to minimize such interferences, which could led to bad throughput and therefore unsatisfying end-user experience. Furthermore, if you plan to use repeater mode on the CPEs in order to distribute the signal to the end-user's devices, you cannot use TP-Link's TDMA technique to avoid such interferences, so the maximum number of end-user's devices is limited purely depending on the overlapping WiFi cells (if they overlap at all).

To give more tips for a possibly suited setup using CPEs, I would need more information on your specific use case, a map with the locations of the APs, distances of the CPEs to each other and distances to the central supplying AP etc.