Durability in leather really doesnt have a whole lot to do with weight. With proper care any well-constructed article out of ANY weight of leather can last a lifetime and more. On my saddle bags I use up to a 13 oz leather. As far as tooling goes, make a rob roy and tool the flap. You could also put the front stiffener on the outside and do some tooling on that. I have considered doing that myself but time usually doesn't allow me to do the tooling.

BB