The router can route many more than 50 devices if it is decent. The issue is the radio in consumer quality routers cannot effectively handle more than a limited number of devices if they consume any significant bandwidth.
If you go to any commercial facility with a lot of users they all rely upon a series of well positioned APs to provide sufficient radios to support the needed connection load.
Your biggest problem would be using only 2.4 GHz in a confined area would limit you to three channels (1, 6, and 11) or you would have interference issues that would adversely impact overall performance for users.
Perhaps if you share more information on exactly what you are doing it would help. Why only use 2.4GHz? Almost all modern devices also support 5GHz and at the short range you describe that would work well with the many users in a confined area as there are more channels to use