I would think the average backset in a Hill bow would be around an inch. The form would probably need a little more as the bow will relax a tad. For a string follow, just build the form straight, the bow will take a slight set and you will have a string follow bow. The reason some prefer a string follow, is that it may act as deflex, possibly making it more accurate and definately quieter. Some serious string follow builders will glue up the lams alone reflexing them the opposite way, then glue the bow up with the limbs being pre-stressed for better performance. I always chuckle when I see someone say how quiet a certain string material is and their bench mark is a string follow bow.
With all the supposed improvements made in stickbow archery we hear about today and the people that promote it, when they can match the feats of Hill, the Wilhelm Brothers, Andy Vail, Russ Hoogerhyde and others did with wooden bows and arrows, then I will listen to them...