I really like this, the sound of a 12 string is fantastic and it's not really used enough in my opinion.

If you do bulk it up with other instruments I'd keep it to just a basic drum part and a simple bass line which loosely follows the chord progression, It'd really just add some variety and "oomph" to the song.

Good luck throwing lyrics on it, I'd like to hear a finished version.

Too much gain = Ears in pain