Start out simple. For a 28" draw, build your bow 68" long, 1 3/4" wide(MOL)at the fades and out 8" to 10" then a straight taper to 1/2" tips(for now). I prefer to have the center of the handle the center of the bow and equal length limbs. This set up is easier for me to see good tiller with both limbs bending together.
George Tsoukalas' website says to build a bend through the handle bow first. That is also good info as is the rest of George's site. You can find a link to Georges site at the top of the "How To" page.
Post lots of pics and ask lots of questions before you jump into that hickory. It will save you a lot of grief!