I’m surprised there aren’t some great tools out there that help with this. Seems like a niche to fill as it’s inevitable that peoples free storage hits limits over time.
If you are in the habit of exchanging a large amount of documents and pictures over email, a dedicated storage solution might be more appropriate.
Work-related communication, as in freelancing, might deserve a separate mailbox that is kept clean of unimportant things.
I could go on and on for what I'd consider a great cleanup experience. It's surprising to me that such a thing doesn't exist, nor is it the kind of thing that's built into Gmail itself. You'd figure they would be best to offer a simple cleanup experience that has sane defaults.