We recommend hosting sessions of 100 users (or less).
This is not hard-coded, you can have 101, 102, etc. The more users in the session, in general the slower the updates will occur in the BigBlueButton interface.
If you are going to host a large session, we recommend only one person (the presenter) share their webcam. If possible, upload the presentation as PDF and share the slides (as opposed to using screen sharing).
Overall, for best performance, we recommend 100 users or less.