What a great choice you have made to model the design on HRH's sporran.
Your thoughts on doing away with the petals that you see on every other hunting sporran are splendid. I think you should also stay away from tassels and a metal cantle as these seem to be everwhere you look. In my opinion a hunting sporran should be not adorned with flashie tat. It is a workhorse that should not attract undue attention. I really like the idea of the pinched leather under the targe design

As for your comments regarding the stiff board front or lack thereof on HRH's sporran. I believe his sporrans are many many years old and may have lost some of the stiffness through use (I understand that they were given to him by one of his uncles)