How to LOCALLY backup/save gmail via intermittent Google Takeouts for future viewing with TB?

I would like to purge some space from my gmail account (just the emails). I know I can create a Google Takeout, but am new to TB. If I intermittently create Google Takeout .mbox files is there a way to intermittently add them to my local computer/backup and view/search them using TB? I don’t want to “sync” because I want to delete possibly >15GB from various gmail accounts, but have them saved (not deleted) locally.

If so, how do I create separate “boxes” for all of my different email addresses?
Many thanks.