I'll ll take a shot at answering your buttplate question. It is difficult to describe in words, not that hard in practice. After cutting the basic curve of the buttplate into the butt, you will inlet the entire buttplate pretty much from the heel first. To start, I place the buttplate against the stock and roughly pencil around the outline of the plate itself. Then, staying well inside those lines, I remove as much wood as possible, it is pretty much an eyeball operation at this point. Then it is simply a matter of using your inletting black, soot or method of choice to mark your plate and tap onto the stock. You will want to approach the inletting by bringing the plate down toward the heel area first. Before removing any wood, though, take a look and be sure you will not be removing wood that will not be under the plate itself, as the plate settles into position. Don't just go chiseling away all the inletting color you see without thinking first. Like I said, it is easy to demonstrate in person, hard to put into words. For those of us that are technically challenged with computers, cameras and all those modern gadgets, it is even harder to explain.
As far as thumbpieces , there are two ways, both HC. Some have a lug cast into the bottom and are then threaded and a hole drilled down into the trigger plate area and a small bolt holds them on. The other method , which I prefer is to make nails out of silver wire/rod. I chuck about a 1 inch length of about 1/16th inch silver into my drill press and using a double cut file, make a tapered point about 1/2 inch long. By using a double cut file, you will create tiny ridges in the nail, sort of like a ring nail that will hold the nail securely in place. Then, I drill however many holes using about a #55 drill bit in the inlay and using a countersink by hand, make a small chamfer in each hole. I place the inlay in place, and drill a pilot hole with about a # 60 or # 62 bit. Cut the wire to slightly longer than needed and drive in like any nail. If you lightly tap the protruding part, it will peen over nicely into the chamfered hole and be almost invisible, although I like the slight outline of the nail head itself.
I hope this was understandable. I really need to learn to post pictures! I am so computer illiterate. I guess that is why we build rifles that went out of fashion 175 years ago!