Thanks guys, I think I have (finally) decided!

I'm going to buy a decent external backup drive using ext4 for documents, photos and music, and then I'm going to cross all my fingers and toes and give BTRFS a spin. If (when?!) it eats all my data I'd probably lose a ton of video that I've already seen. Annoying, but not the end of the world. The whole exercise is probably a good push for me to create a decent/better backup system too.

Wish me luck!