Amon mask (need molding help)

I am currently working on an Amon costume and I just received my 3D printed mask in the mail. I plan on making a mold of the mask, but honestly I have no idea how to go about it.

I've never molded anything before and I couldn't find much information specific to molding and casting masks. I know I'll need to slush cast it, but any other tips or recommendations (e.g. what is the best mold rubber, what is the best casting plastic, any other materials that I need, etc) would be greatly appreciated.

Here are some images:

my 3D model:


the printed mask:

What you're wanting to do looks (to me, anyway) very similar to the process PredatrHuntr used to create his front plate for a Predator helmet --> http://www.therpf.com/f62/sculpting-2-predator-bio-helmets-153152/


Hope that might help a little.

That's exactly what I was looking for. Thanks for the help!