Have to say thank you for really taking the reigns on this Beaverslayer. Though don't see myself buying a gun, and going to town, stranger things have happened and I can see the potential in this.
My thoughts on leather, have you tried one of the waxed upholstery leathers?
On dyes, you said you were working Tattoo dye, have you tried acrylic paints, Tandy cova is marketed to the leather working community, but I know Liquatex is more aimed at the art/painting demo, and is known for density of pigment, and consistancy. There would be a different learning curve with handling, and effects, but I could see where it would be good from a working, and colorfastness standpoint.
Just a couple of cents..