I have not built any branch bows, but my guess would be with only 4” diameter to work with, I personally would thin one side down to near limb thickness, except for handle area if you want a 1 piece handle, and strap it down flat to dry. Rather than get greedy and end up with nothing, I would try to get 1 good 1/2 out of each branch. Hopeful someone with actual experience with small diameter branches will chime in.