Questions about Latex Casting

Hi all, I joined this forum as you seem a knowledgeable bunch and I have some questions about casting latex.
I'm making a pony mask that will need to be flexible to put on and insert a bridle bit into the mouth of, but firm enough to not buckle when some pressure is put on the reins.
From what I've read, latex can realistically only be cast from a plaster mold - how many masks do these plaster molds tend to produce without wearing down/breaking?
Would it be sensible to slush cast the latex in them? It will be expensive to be buying enough latex to fill them ever time - especially since some masks will be different colours.
The faster the turnaround time the better, as I plan to be selling these masks en mass, with options for customisation.

Depending on what stone you use and how you mix it you'll generally get around 15-20 good pulls out of a stone mold. Sometimes more, usually less. If you plan on making anymore than that you should make a master copy... a much thicker pull that holds its shape, used to make more molds.

If you slush cast it is easier to do it in layers, I've found. Do a thin layer, leave it for 30 mins or so, then repeat until you have reached your desired thickness.