Which Object Support Teams?
Account, Opportunity and Case.
Creating a team member in the app creates two records: a team record and an associated share record. If you create team members programmatically, you have to manage both the team record and associated share record.
There is only one team per record (Account, Opportunity, or Case). If multiple teams are needed, depending on your specific needs, consider territory management or programmatic sharing
https://developer.salesforce.com/docs/atlas.en-us.dat.meta/dat/dat_components.htm
How can a user setup a default team?
User setting -> Advanced setting - > While defining team, access level for account , opportunity and case object can be defined.

Can teams be managed out of Salesforce?
If teams are managed externally, say through an external commission or territory management system, then integration can be used to manage the account team. There are cases when territory management in an external system can align with a team solution within Salesforce.
Who can modify team members?
Record Owners, Roles higher in the role hierarchy or Admin. They can update existing team member record or add new members. A Team member with Read Write access can add other users to team who already has access to the record. https://developer.salesforce.com/docs/atlas.en-us.dat.meta/dat/dat_components.htm
Teams Use Cases?
Major considerations