I have 2 questions

Let me try answering your questions as how i understand them and probably later on based on my answers you can get back to me if i did not get you right

1.I want to limits the number of viewers per stream:-

You can use Authorization Plug-in to achieve this solution.

You can write a logic which keeps track of count of number of plays each stream receives using E_PLAY event. Now when you have reached limit for particular stream you can deny request for the play by not authorizing it in Auth Plug-in.

2. I want to limit the valid stream names

Again, you can use Auth Plug-in for this use case. Define your set of valid names and whenever anyone tries to publish a stream, check for the stream name in E_PUBLISH event and depending on whether its valid or invalid , authorize or deny it respectively.