Can I play a song from spotlight?
Maybe not default Apple feature, but is there a flashlight plugin for this or something?
Yes, you can do this natively.
Just open Spotlight as you normally would (e.g. use the commandspace shortcut) and start entering the name of the song. Spotlight will find it and you can just press enter to play it.
You don't need to have iTunes running at the time you conduct the Spotlight search, but you do have to have the song stored locally (i.e. not in iCloud), otherwise you'll get web search results etc instead of an iTunes result.
You also have to ensure you have Music selected in the Search Results tab within Apple > System Preferences > Spotlight