I purchased a large piece of leather (full hide) from craigslist for cheap so I will make a test chest piece with it before making it with the good thick leather I have.
How do I get the shape molded for the pectorals? I've read about wet-forming but what would use/make as a mould? You could make a foam mold, or emboss the leather
I'll try the foam mould then first and see how it goes, if it's not forming right I'll try using something else like a piece of wood.
The chest seems to have a split down though the center to the bottom of the pectorals, I assume this is to be able to get in and out of the armor? You're reading too much into what you see. The armor is fantasy. What you see has nothing to do with purpose or function, it's all fantasy. The design, layout, methods of attachment, etc., are all fantasy, and are not similar in any way to any type of historical armor.
From what I have read the game designers did try to make the armor "functional" and kind of, sort of, historically based. Though I will agree this is fantasy armor and there will be many things that are pure imagination just because it looks cool. I made a thick paper version of the armor to test on, and as I suspected I couldn't get my head into the opening without making a slit.
Do I need to put metal eyelets in at the shoulders for the lacing? Not necessary, since the suspended weight is minimal and you won't be fighting. Just be sure that you set the eyelets in the leather far enough away from the edge that they don't rip through.
The sides come together and attach with clasps under the arms, It looks like it's a perfect fit but should I make it slightly overlap instead? Yes, that makes it easier to adjust and fit properly
The neck has a collar that comes up, how do I make it so it attaches all around? How do I attach it? Historically the neck protection was a separate piece (in most cases), worn under the chest piece, not a collar. Again, since this is fantasy you can make it and attach it in whatever manner you want.
Understood, but how should I make the collar?
Question: For the edges which hold down the chainmail, do I cut one set of the side pieces short so that they don't overlap? or do I overlap them? Don't understand your question
Sorry, that wasn't clear. The shoulder pieces have thin strips of leather that surround the chainmail. If all the strips extend from edge to edge, then there will be a small section in each corner that will have 2 strips overlap. I'm wondering about how to keep that overlap to a minimum.