Question about foam latex and casting

I'm shooting a short horror film and I only need to make hands for the creature. The idea was to cast the actress' forearm (up to the elbow) using Alja-Safe and Smooth Cast 300Q, then using clay I'd create the creature's forearms in clay over her hands and then cast that in foam latex to make a sort of arm sock/glove and be set...my question is, is foam latex the best route to go for this? Also, if I'm casting on the actress' forearm it should fit perfectly, but what's a good thickness to go to prevent tearing? And is there any risk of shrinkage?

I've never used it before and since this is DIY can't really consult with anyone regarding it outside of you cats who do this on a regular basis. So, thanks for any help you can provide.

Also any critique of my planned outline is MORE than welcome.

You'll want to use something other than the smooth cast for the core, since it won't withstand the heat of baking foam latex. Repro, 1630, or even ultracal. Usually you want to design it so some of the fingers are collapsable. Otherwise you'll have a heck of a time trying to get the wrist of the glove over the spread fingers of the core.

Typically people will do a thin layer of wax sheet to create a uniform minimum thickness, and then sculpt on top of that.

You can put a spandex glove on the core before running to give it more strength. You will get shrinkage. That's just the reality of foam latex.