[Darryl Ramm]

Yes you need to format the drive.

Yes you should enable TRIM using "sudo trimforce enable". Google it that if you have questions.

With High Sierra or Mojave I woud be formatting the SSD as APFS, on Sierra meh it's more of a thought process, but probably yes (I'm not aware of any serious bugs but it was newer on Sierra). Or if you need older systems compatibility then just use HFS+.

Adding new drives is often good time to try an upgrade. You can throw MacOS Mojave onto one of these drives and try running it from there for a while and then switch over if it works well.