We made the same decision. Our accounts are user owned as long as the account is not synchronized with the ERP system. In this case the account is always owned by the main sales person of this region.
All users can see and edit all accounts an contacts (accounts only if they are not synchronized).
If you want to restrict some users to teams you can also create sub business units where you put the users in.
- BU Main
+ BU Sub Team One
+ BU Sub Team Two
Hint:
If you just want the team users to see mainly their accounts and contacts I would prefer to install the "Activity Feeds" addon. This addon adds some interesting "Follow" buttons. If you click on this buttons in a contact form this contact will be flagged for the user and will be visible in his "Contacts I Follow" View. If this View is the main view for this user its possible to edit and see all contacts but you can also restrict the view to see only the contacts your are currently working on. But this has nothing to do with rights!
Thomas