Hey there DollyKim!!
Is this your second try after giving up on the modded Craig head from the PTE line? He came out really good!! What sort of clay are you using? Have you ever tried super sculpey? I find it to be the best balance for people like me who aren't MASTER sculpters but we can put together something and you know what it is. It stays "wet" until baked in the oven, and with sculpting tools you can get some gorgeous smooth edges in. Some sculptors use apoxie, but unless you're making something super small that can be done in under four hours or using it to sharpen up edges on a baked sculpey sculpture (apoxie can give you rock hard, thin edges, great for delicate things like modified elf ears, etc), I would stick with something like sculpey.
Sculpey also allows you to make things much smoother and cleaner where they need to be, like the skin.
Advice aside, I'm quite impressed!!! I'm still putting off Maes Hughes' head because trying to turn Full Metal Alchemist characters 3D is like pulling teeth from an alligator. I had to buy a few Japanese gashapon toys as references. Out of curiousity, how did you figure out the measuring process for his neck width?