Always create an overall top umbrella team representing the Organization. This can be titled "All Users", "All Employess", etc. https://www.screencast.com/t/IkVjboUA. This will all you to do overall team assignments/unassignments to all users, create additional side teams and allow for scaling. You might not ever find a reason to use this umbrella team, but if the situation occurs where you do need it, you will be happy you created it! There is no negative impact to having this team exist.
Learners can be on as many teams as needed. It is very common to have learners on multiple teams at once for different reasons. For example: You may have your users on the "Customer Success" team to recieve training on their daily duties as a CS Rep, but also on the "Fast Track to Management" team to work towards their internal career goals.
There is no limit to teams. Teams are ultimately a grouping of users. This is a tool to allow YOU as an Admin to organize your users and group them together to easily perform group assignments of courses in Litmos and allow yourself easier and more efficient reporting. Do not be afraid to create teams for things such as "manager" teams. "New Hires" teams for new employee onboarding, etc.
User can be different access levels on different teams. For example: Your Sales Manager may be a "Team Leader" access level on the "Sales" team, but this user might be a "Learner" on the "Manager" team. We do not want this user to run reports, assign courses, or see how other managers are doing on the "Manager" team. They need to simply do the training assigned to them on the Manager team. However, I DO want this user to manage the "Sales" team. This works perfect and is very common.
Make sure you buckle down and fully understand your Team Leader/Team Admin access levels under "Accounts > Roles and Permissions". Determine what you want each role to do, test this, and then begin promoting users to these access levels on teams. Remember, these roles and permissions are customizable.
To demote a user from an Access Level on a team, you need to click the "X" to the right of their name on the Team Leader/Team Admin list view: https://www.screencast.com/t/kVQIuimi
It is completely okay to assign learners the same training through various teams. Learners will not know this is happening and they will not see duplicate courses on their Learner Dashboard. Additionally, if they completed the course previously, the completion will stick and they will not need to re-do the course if it was already completed