I'm doing a cake with cut outs or stenciling of a horse,from sugar paste.
I did have a practice go,but the edges were not very neat and horse looked terrible.
1.How thick should I roll paste out.
2.Should I let the paste dry a tad before cutting.

I find that if I do my cut-outs, it helps to cut them and then take a little shortening smoothed on my finger and go along the edge of it to clean it up. Kind of like you are smoothing the edge. Some areas you may have to kind of gently 'rub' to get the look you want. Also, using an exacto knife helps keep it cleaner.
I don't really give them a time limit to dry, but the shortening on my finger helps them smooth out if they've been out for too long. As for the thickness, if I am making it to stand, I go about 1/4 inch. If it's going to be pressed on the cake, less than that. HTH!