all mikrotik devices have no limitation for number of clients. the only limiting factor ir 802.11 standard and physics.
normally I would suggest to keep the connected clients below 100
That's not an easy question to answer.
Theoretically hundreds of clients could be registered but that does't mean it would be functional.
regardless of chosen vendors equipment, factors such as antenna (both ends), los or lack of, fresnel zones, interference, neibouring wifi installations, distance to and between clients, hidden node issues, chosen wireless protocol(802.11 nstream, NV2), current channel usage ....The list goes on
but basically many factors need to be considered and conveyed before others might be able to provide experiences about qty of registered clients and usable throughput seen in real life etc.
If you could explain more about what you are trying to achieve, it location and other factors that have influence then others may be more inclined to chip in and share their input.
Thank you for your direct replies. I want to use them as: ap bridge mode, 2GHz-B/G/N Band, 20MHz Channel Width, 802.11 Wireless protocol. I have a vdsl 50Mbps internet line. I don't care about the unique bandwidth per user if there are many clients connected. I just want to know the max capacity of Concurrent Clients that can be connected and these devices can handle with the above setup.