I usually put them in /media, so my games drive for example lives in /media/games.

Seems to mostly fit with the usual external media that gets mounted there.

You can just make a new folder, I put mine on /data

/mnt is reasonable and normal. I have used /mnt, /data, /media for various hardware and software mounted storage. It really doesn’t matter unless you’re dealing with some specific software or organization with esoteric requirements.

/mnt or /media usually. I use /mnt for permanent filesystems and /media for removable ones but there are no hard rules. My home folder is a separate filesystem from my rootfs, just depends on how you want things setup.

You mount them to /proc for extra spiciness