Great project to start on. I don't know about the granite top. Might be OK-depending on the color and if it is sealed and impervious to glues and head cements. I'd suggest a laminated Formica top with a backsplash. Extra depth (36") is pretty nice. I have one work station made isng a nice looking finished 48" wide countertop that I picked up at Lowe's for a deal and put it on top of two plastic drawer organizers and that gives me just enough room to get my legs under; plus ten drawers within easy reach. I feel the ideal tying position is with the bottom of the table right on your thighs and with your feet flat on the floor and the small of your back pressed into a nice chair back. This way your arms are not rased too high and there is less fatique. Keep the arms low as possible.
One thing I'll suggest is that you inlay a sheet of steel flush into the table top. Alternately-a thick plate of steel on the table top held down by its own weight. Use either polished or painted-both fine. It needs to be magnetic steel. Could be only 8 inches square. You put this near the vise-off to the side. Those magnetic sheets with the adhesive backing-cut a piece to fit the underside of the super glue bottle and head cement bottle. Stick them to the bottles. Now the bottles will stick to the steel plate via the magnetic "shoe" yet-removes for use easily; and it will not ever spill or tip over! You can put a smaller magnetic sheet (no adhesive on it) on the steel plate to use a hook holder for loose hooks being used on a set of flies. Think about a lazy susan on the bench with storage for spools of thread and tools. Cabelas sells a nice one and if you work with wood and have a lathe-you could make one too.
http://www.americanworkbench.com/americanflytyer.html
Lastly-have you ever looked at these benches above? A bargain for what you get. If you like woood-then these are great. I have the very one pictured. FYI