The density of both woods makes it hard to say exactly what dimensions, but if I have picked the woods I'm making it 1" wide, and tapering to 1/4'-3/8" tips. The maple thickness shouldn't be a problem if the Ipe is sound, and like mentioned, is Ipe. So lay out the lines at 1 1/8th, and 1/2" tips and this gives you a little leeway for the cut.
If the Ipe is dense and the maple isn't, its going to follow the string. Don't worry about this, just concentrate on getting the best bow you can..
Rich