If you're going to do it by hand, first thing to remember is that sanding where the curves run with the grain, such as the widest part of the bouts, will go much faster than across the end grain, such as near the tail, especially so with spruce. But you probably knew that. I learned it when I got my first oval soundhole without even trying.
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I start with a new piece of 80 grit, about a 1/4 sheet, folded to three thicknesses to give it some rigidity, but not too much. I'd start with the back, because it's probably a harder wood with more homogeneous grain. Position a work light so that it will cast a shadow on the edge. Hold the sandpaper so that the middle of three fingers provide the force. Holding the paper at about 45°, sand gently until you have a bevel that goes down to half the thickness of the back or top. Use the shadow to gauge your progress. Curve the paper appropriately at the curves so that you avoid a small contact area.
You're about halfway there now. Switch to 100 grit, fold it to three thicknesses, then knock down the edges of the 45° bevel, rounding them until you get a good blend. Work down to your desired grit. Don't go past the thickness of the plate on the sides - the rounding shouldn't extend past the plate. Also, try for a definite end of the flat area and start of the curve, not "tapered," unless you want a home-made look. Keep some stiffness in the paper to avoid ripples from the grain, especially on spruce.
Nice looking instrument so far. Good luck, post pics!
Pat
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