Backups seeming much much larger than my hard drive
It's a glitch in Time Machine. When an auto-backup is scheduled but your external hard drive isn't available, the computer saves a backup locally. I'm not exactly sure how their space-counting function manages to mess up like this, I'm just paraphrasing what I read in a Google result that then proceeded to give me the solution that worked for me.

The solution: Go into System Preferences > Time Machine, and flip the switch from on to off. Restart your computer, confirm that your storage usage looks reasonable again, and then you're free to go back and switch automatic backups on again.