All the materials you list are quite durable, that includes the shell. Micarta is material soaked and pressed in resin, usually paper, linen or canvas, also very strong. Good luck with your endeavor.
I have never had a problem with engraving the sheilds nor have I heard of any problems from other knife engravers. However if for some reason it did pop loose, just superglue the shield to a plate of steel, finish the engraving and the maker can just epoxy it back in when you send it back.
Learn the fundamentals of ornamental design. The first part is understanding how to draw the backbone of your design which is the framework everything is built upon and then you start adding your leaf elements. All the info is out there in the form of books and forums you just need to sift...
Try posting this on the main forum, better chances of getting views and responses. Good luck with your endeavor.
Thanks all for taking a look and the kind words. Be well. B.