@GKR 

Hello, the maximum No. of associated wireless clients for each band will be 127.

However, we will not guarantee nor can we give you a precise number that you can connect, the maximum number of concurrent clients which wireless routers can handle is mainly restricted to router hardware and network environment. The specific number depends on the summed up traffic that is generated and the bandwidth given by your ISP. For example, if some clients in your network are doing uTorrent/P2P downloading or playing online games, most of the bandwidth and system resources will be occupied, then only a few clients can enjoy the network; but if all the clients just do ordinary web browsing, or generate extremely little traffic, then the router can handle much more clients simultaneously with good network performance.

You can remotely manage the router via the Tether app, or you can enable the remote management on its web GUI as follows:

https://www.tp-link.com/support/faq/1553/

Regarding the MAC filtering, I think you can use Access Control to achieve that:
https://www.tp-link.com/us/user-guides/archer-ax50_v1/chapter-9-network-security#ug-sub-title-2