we make shoulder bags that hold 6 full bottles of wine at once plus 2 lbs of chill packs. They have hand straps to carry also a shoulder strap that connects to 2 d rings one on either side of the bag. we mainly make them out of 600d, 1000d, 1680d ( ballistic nylon) but we do make them out of leather (chrome tanned)as well. when we make them out of leather for the shoulder strap we use a nylon webbing that is sewn on to the underside of the leather strap. gives great strength. as far as taking the thickness of leather into account, if you cant skive the edges.... then its going to be thick not sure of a way to thin it out per say. ??
Keep us posted
Best,
Ben