There’s also the issue that around once a year the two planets will be on opposite sides of the sun. Not only would you have a lag of close to 3 hours, but communication would be completely impossible for a month or so at a time.

Yes, but the two-and-a-half hour lag each way would be a killer.

You could check out FolderFort. Sometimes they have lifetime pricing. I paid something like $170 for 3TB lifetime.

They have SFTP access in beta.