Miscellaneous topics that do not fit into specific categories.
An iCloud address can be used as a Microsoft account's address, but then it's just a username and is not tied to iCloud in any way. In fact, you should not use the same password for iCloud as for the Microsoft account.
Your Microsoft account should remain the same throughout. If a Microsoft 365 Personal or Family subscription lapses, the account will revert to a free account with the storage limits of a free account. You can then subscribe to another subscription or renew the one you had to regain the storage limits for the new subscription. You may have to update your location information within the Microsoft account at https://account.microsoft.com/profile.