@johannes_jahn free Trello teams can have unlimited members in the team and unlimited members on boards, but are limited to 10 boards per team.
If you need more than 10 boards in a team, you need to upgrade the Team to business class, which means you will pay for each team member, and each board member who belongs to more than one board (a "multi board guest"). You can see more about billing here:
Hello Community! My name is Brittany Joiner and I am a Trello enthusiast and Atlassian Community Leader. I'll be sharing with you a series of videos with my top tips on how to best use Trello...
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