But when it comes to the headgear, I believe you only have to replace the shaders of the plumes. The rest should be the already used "specular_shader_skin_bump_high".
I have not that much knowledge with all the shaders, so what would be good additional shaders I really couldn't tell. Your best shot is to look for an already OSP or something that includes plumes, or a mod's brf file. And check the shaders on those and see if they work.
Use specular_shader_skin_bump_high if it's rigged, specular_shader_noskin_bump_high if it isn't. If there's no specular texture (like most cloth models), use standart_shader_skin_bump_nospec_high or, if it's not rigged, standart_shader_bump_nospec_high.
The rest are fairly rarely used for armours and you'll only come across them if you want to do something similar to another specific object in warband -- for example you use flora_shader to make new grass or leaf materials.
You need to change the code settings to make the hair invisible or use bald on the top style hair. It's because these resources are designed for Napoleonic wars where all the hair is bald on the top so it doesnt clip, but native hair will clip.