Please help with IMAP/Mail. There's no info anywhere :(

Hi guys, begging to find out. I'll express summarize.

Desire: To access multiple outlook & gmail accounts through the mail app. I want the mail app to function as a portal. I don't want it downloading emails locally, however so long as I have an internet connection I'd like to be able to access any emails from it directly through the mail app. Even better would be to select specific emails to store locally (important ones), and the rest staying on the server and not using my disk space.

Problem: IMAP info is scarce and difficult to understand, I've tried limiting IMAP folder size to 1,000 from Gmail - however I still can't find out if this stores locally or not?

I really hope someone out there can help me! Thanks so much for your time.