Resin noob here, can somebody help?

Hi! Ok so I think I've watched all the tutorials possible for resin building. Enough to convince me to try it out, but I still have a lot of questions regarding materials.

Where can I get a good mannequin head for sculpting? Last time I checked the monster makers one was out of stock or whatever---oh hey!! They got this guy in stock! http://www.monstermakers.com/product/deluxe-full-head-sculpting-armature-life-size.html :D

Ok so his head is 23" and my head is 23" so that's good! So if I make a sculpt on him and cast it it will fit me? Will I have to alter anything?

Another question I have is what EXACT type of clay and resin to get and where to get them. I've gone to art stores and whatever but not really sure if they have the right stuff, or if I just don't know what I'm looking for. I heard I need sulfur-free clay, but all the clays I saw at the art store didn't have ingredients or anything that would indicate if it had sulfur or not.

And I think I can figure out what type of resin to use, so should I just order it from Smooth-On's website or do they sell it in any local stores?

Sorry for so many questions! I really hope somebody can help me out, though. These questions have been bugging me for a while.

Thanks for reading :D