As I know, there seems no official method to achieve that, maybe you could try some third-party add-ins in Outlook to see if it could help.
Calendar Tools for Outlook
Personally, I would more willing to use Exchange email account and Archive emails which I need to local disk.
As I know, there seems to be no option that could combine multiple accounts' Inbox directly in Outlook, Search folder could only search these messages in a specific account. So in order to meet this this requirement in the future, we could vote for this idea about the Unified Inbox feature in uservoice for Outlook.
Also, based on my research,as an ...