Hi Muni,
The creation of Business Units is driven less by your organizational structure and more by the need for the visibility of records to be limited. The only reason to create a business unit for any group is if one or more users in the group should ONLY see records owned by others in the group.
Let's say my organization has 30 teams, and 27 teams should see all records owned by all users, and 3 teams should ONLY see records owned by their own team, then I would create 4 business units.
If each of your sales teams should only see records owned by other users on their teams, then you may have to create 500+ business units. Alternatively, records may be owned by Teams and not the individual users. But if there are not restrictions on visibility of records, then you may not even need the Business Units you have already created.