Lee, I think your decision on limb tapers will effect the smoothness of your draw more than the riser length. IMHO The riser length will determine the forgiveness of the bow, physical weight, pointability, and other shooting aspects. .001 tapers will give you a bit smoother draw over .002 tapers, so when your planning your pack laminations, I'd take that into consideration.
As far as limb pack thickness, check out binghams website for there thickness chart. It will help you get a baseline for your first build, IF you use there R/D plans. Tim