What rules does OS X use for naming mounted volumes?

1. Yes, this is standard OSX behavior. If you have two identically named volumes, OSX will suffix 2-N with a digit in the filesystem (however, I don't believe they appear differently named on the desktop)

2. OSX mounts everything under /Volumes/. You can see what the interface is by running the mount command. Physical volumes are mounted in /dev/diskXsY, where X and Y are interface ID's.

3. ¯\_(ツ)_/¯ - you asked it in the Apple area.

1. Yes this is standard behavior.

2. & 3. Are in part covered by what's quoted below from Mac OS X and iOS Internals To the Apple’s Core by Jonathan Levin published by John Wiley & Sons, Inc.

Other then the mount points defined in the Automounter master map and /etc/fstab, if present, all other mounts handled by OS X take place under /Volumes/.