how legal is this?

Not (depending on where you are). However, in my opinion it is absolutely ethical.

Do you need to hide in complicated ways?

Depends on where you are. For most people, yes you need to hide it, but it needn’t be complicated. You can just bind your torrent client to a (trustworthy) VPN.

That said, these things always carry some risk, and that’s yours to take.

Mirror a couple TB of anna’s archive

I’ll be fine using mint… Right?

Probably! Best way to find out, is to just try it out :)

Y’all are good at making this sound very complex.

Fwiw, this isn’t really aimed at people who are just dipping their toes in. Enthusiasts in any field can sound insane from the outside in