[shiroiuma]

I'd recommend a USB-connected external hard drive (not SSD). You don't have very much data, so a thumb drive could probably hold everything, but SSDs/flash aren't great for long-term data storage and will lose their data if you don't power them up and use them now and then. An actual HD doesn't have this problem, plus they're typically 1TB+ so you'd have plenty of space for future needs.

Alternatively, you could get a handful of flash thumb drives and back up onto all of them, syncing with a different one each week/month/whenever so that they're all getting continuously refreshed and you'd have snapshots in case you accidentally delete something and that deletion gets synced to the most-recent drive.