Twitch doesn’t apply a rate limit to “reading”
The only limitation is your ability to keep up.
Twitch will disconnect your “bot” if you can’t keep up with the message queue and the send buffers Twitch’s side gets too full.
So really depends on how many busy channels you connect to and how good your code is at keeping up.
You’ll have to expand as you go and see if you can keep up and adjust accordingly