Have spent today and most of yesterday trying to workaround what appears to be a bug in the Godot sound causing glitching. Finally have a working solution:
I'll fix up some decent different sounds, these are just for testing. And I figured out the audio buses, I now have 3 buses, one for short reverb one for long and one for music. I've adjusted the view angle a bit to make things appear more 3d and put in shadows, and replaced the player box with my frog from my frogger game, this is just temporary though, will probably be a spaceship. And I've put in some kind of scrolling background, just a plane will do rather than skybox as the challenge is for a 2d type view.
I discovered by accident that it was quite easy to make spinning static physics objects. These will make great obstacles, I'll have some spinning and maybe some like moving platforms blocking the way. 
Will the frog be the captain of the ship?