there is no problem in using an image as an background-layer. Your Project should use the dimensions of your picture, so you don't have any black borders around.

Particles funktion in an 3D world so you can rotate them as you like etc. Leave your image 2D, so it's always orientated towards the camera. Perhaps you have to use some masks on the particle layer, if you want them starting behind an object on your image or so.

good luck!