Windows does not like ext4, and servers does no like external drives. I used few years ago similar setup but with ext4 and few times due to some usb issues or something lost all data… So, I moved to more native and robust solution. Any way, there is also something to do after you move your data, there is a big topic about it: HowTo: Change / Move data directory after installation
And here discussion about snap user: External storage (Local) NC (snap) -- user www-data or root?