Hi @Caspar - ABO
Based on your description, we recommend that you create 6 teams and 6 private channels for each team.
Shared files for each department can be saved in the team's General channel (which is automatically created when the team is created), and files in subfolders can be saved in separate private channels.
Each private channel has its own SharePoint site. The separate site is to ensure that only members of the private channel can access private channel files.
For more information about teams and private channels, please refer to the document:
Overview of teams and channels in Microsoft Teams
IT Admins - Private channels in Microsoft Teams
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