Kanuns wrote

I'm planning to use CPE 210 as an access point in my open area. I wanted to know that how much Maximum clients/users it can connect.

Throughput and maximum clients depend on many factors such as usage patterns of the users, existing APs in the neighborship sharing the same frequency band and whether MAXtream TDMA is used or not. According to TP-Link's Pharos website the WBS and CPE can support more clients (or more precisely: a better throughput among the same number of clients) if MAXtream is used, but since it is a proprietary protocol smart phones or other devices don't support this feature. Following diagram from the TP-Link website might give you an impression of the limit for maximum clients if you take into account the impact on the CPE's throughput:

Next point is the type of clients: If you want to supply mobile phones, be aware that the CPE has been designed for directional links and thus has directional antennas suitable for very long ranges. Clients such as mobile phones don't have such antennas, so when sending back data to the AP their range is limited to a much smaller range.

For supplying WiFi to mobile phones I would clearly prefer the EAP225-Outdoor, which is a dual-band AP with two external omnidirectional antennas capable of MU-MIMO. This AP should be able to supply much more clients than a CPE (around 60 to 80 for the EAP225-Outdoor if I remember correctly).