I have a Mac, and use Time Machine, the built in backup software, to do hourly incremental backups to two external drives, one of which is a dedicated backup drive. This means when one fails, or my Mac fails, or even if my Mac fails the exact same time as a drive, I have a backup. It's kept me going through a few drive replacements and one computer replacement.
So I would recommend that, or whatever the equivalent is on your platform. Backup everything as you never know until it's too late what's important, and it means when your PC dies you can restore from backup once it's fixed or replaced.
Github certainly supports private repositories. It seems a bit unwieldy for backup though, unless it's already part of your workflow. I would instead just zip it up in a password protected archive, which you can then put in multiple places; dropbox, as an e-mail attachment, on a SD card in your pocket or phone. So when the meteor strikes your studio and turns your PC and drives to dust you also have a backup or backups elsewhere.