The only thing I'd be concerned with is trying to make the collage work visually with too many different kinds of frames. I'm thinking the color and style of the frames should be the same (or at least style, but I'd need to control which parts of the collage had which color). On the other hand, it will be hard to make it work if too many of them are the same size. I think it will look more organic to have a lot of different sizes somehow fitting together.