Hi Spyros, my name is Jose. I'm an Independent Advisor and a Windows user like you. I'll be glad to help you today.
A tenant is the official name for a Microsoft 365 organization. You can identify a Microsoft tenant by it domain that end onmicrosoft.com.
Subscriptions can not be moved or migrated between tenants. The account data can be migrated. In many cases a third party services is required.
A tenant is free. In a tenant under a Microsoft account you can host Teams free, Azure (many services are free for one year) and Office online.
As I said before, tenants are free. If you have a good internet connection and a computer to connect to the services, you don't need any other prerequisites.
Are you planning to roll out Microsoft Teams free or Teams for business?