Vincent, thank you for your prompt reply. I am indeed confused. Based on what i have seen so far, O365 Enterprise E3 is the only plan that supports both legal hold feature and the use of Outlook for Mac v15.6, as well as the full suite of Microsoft Office applications.
Looking from another perspective, I don't intend to use the full range of Office applications, just an O365 plan which supports the legal hold feature and the use of Outlook for Mac v15.6. From your suggested plans above, what plans besides E3 will best suit my needs?