How Should We Structure Our Microsoft Teams and SharePoint for Multiple Offices?

Consider how your offices operate. If most of them are just single departments or related groups, it might make sense to organize by department instead of location. Think about what everyone will actually need access to—sometimes, it’s more effective to focus on shared tasks rather than just geographical layouts.

There’s some solid advice here, but I’d seriously suggest hiring a consultant. They can help assess your current setup and discuss what will truly work for your organization. And don't skip out on an adoption plan for your staff; I've seen many migrations fail without one.

What’s your plan for private channels? If only office managers have full access to M365 E3 while others are on M365 F3, you might want to focus your private channels around specific Office Suite documents that are important for each office.

I’d recommend setting up a separate site for each office along with a hub site for the organization-wide content. This way, you can keep things organized without overwhelming everyone in a single team. Plus, blocking users from creating their own groups is crucial to avoid a lot of headaches down the road.

Remember that SharePoint Online allows up to 25 TB of storage per site, so if you think any site might get close to that limit, it’s better to separate them for different departments or offices. Just keep in mind that a SharePoint site doesn't have to be a physical location; it can be as per your needs!