How do you add a background to it or non animated objects?

Can you explain this a little more anapasta?
What is your end goal? Are you wanting to add the Grease Pencil fire in front of something else?

Ok - so I think you want to just render it out as an image sequence (with alpha) and then add it where you need it in editing.

Or add your title to the scene and then render it as part of the same image sequence (or still image if you only want 1 frame)

I hope that helps.