Archive Mailbox in Microsoft 365 Business Basic, Standard & Premium

Hi PCMan365,

Good day to you.

For your first concern "i have dedicated Primary Mailbox 50GB and dedicated Archive Mailbox 50GB?"

Based on your Microsoft 365 plan, my answer is yes, they are separately 50 GB.

For your second concern “Archive Mailbox will used size 50GB on Primary Mailbox?”

As far as I know, the archive mailbox and primary mailbox is independent mailbox. Archiving in Office 365 (also called In-Place Archiving) provides users with additional mailbox storage space. After you turn on archive mailboxes, users can access and store messages in their archive mailboxes by using Microsoft Outlook and Outlook on the web (formerly known as Outlook Web App). Users can also move or copy messages between their primary mailbox and their archive mailbox, so the archive mailbox will not use 50GB on primary mailbox. 

For your third concern "Any Requirement to Enable It (In-Place Archive / Archive Mailbox) On Microsoft 365 Business?"

Actually, except the suitable licenses, you have to be assigned the Mail Recipients role in Exchange Online to enable or disable archive mailboxes. By default, this role is assigned to the Recipient Management and Organization Management role groups on the Permissions page in the Exchange admin center. If you don't see the Archive page in the Security & Compliance Center, ask your administrator to assign you the necessary permissions. 

If you have anything unclear, please feel free let us know.

Regards,

Joey