Limit of assistants in a channel meeting

SergioNio The limit is still 250 participants in the meeting, so some of the channel users will not be able to join if you have more than 250 members in the team.

There is an request to get more than 250 participants in meetings, vote for that. Microsoft is working on it, but more votes might give us that feature faster. 

https://microsoftteams.uservoice.com/forums/555103-public/suggestions/37824571-increase-the-number-of-allowed-participants-in-a-m

When then increase the number of participants in a meeting it will probably not allow 5000 (or 10000 that will be the new limit for number of members of a team). So if you have need for so many participants in a meeting checkout Live Events instead.