Weight for leather is measuered by the ounce. One oz. = 1/64". For example, 4 oz = 4/64" or 1/16", 6 oz = 6/64" or 3/16", 8 oz = 8/64" or 1/8". Die and burnish your edges to show good quality.
You want latigo leather for the really big dog collars. Veg tan is kind of OK, but if it gets wet, it stiffens up.
You want to use a die, not a stain. Try to find natural dies as some dogs MAY be allergic to man made chemicals. I am, why couldn't a dog?