Let me add few pointers to start with:
- After that we want to use .NET Nuget package Microsoft.Graph to manage users MS Teams meetings with Bearer Oauth2 token.
Yes you can use this. - Will we be able to manage multiple user accounts of our users?
Its doable with Client Credential flow. But first check out whether the API call supports the application permission or not. - Do we need to have some kind of paid subscription for that?
Yes You need to make sure that subscriptions for your M365 accounts which you're using.