Upgrade licensing is pretty steep
When using the Teams free tier for a non-profit, the step from free to paid is rather steep. For us (5 people) it's to 600 eur/year if I counted right.
We don't need all the parts of Office 365 Business Premium. Planner and Forms are welcome, as might be the ability to have email addresses connected to this work.
But at large, it looks to me like there's no entry level, paid version of Teams, for ...well… small teams. Something like Office 365 Home, with Teams added to it.