One suggestion, too. I find 3 1/4" diameter holes hard to beat (for ankle holes), but I'd love to hear what others are using. A better design would be more of an oval shape, and though more comfortable, that's a more tricky cut. A perfect circle that is sanded and/or padded should do. I think 3 1/4" should secure most ankles, leaves enough room for thicker ankles, but when padded is snug enough even for smaller ankles. Remember, when resting the ankles, there's a bit of a dip because the flesh will compress a little.
Yes, also, as others above have mentioned, it's important to determine what features you want from the stocks and what your main usage will be. Portability and storage is something to consider. Also...comfort, safety, whether it's being designed for another piece of furniture, weight, cost, if the size of the person in the stocks and their body parts is a factor, aesthetics when finished, strength...all good things to consider. A great YouTube channel for the basics is Woodworking for Mere Mortals...you can learn everything about tools, wood types, screws, glue, sanding, cutting, safety, etc.
For locking, I would consider those latches (you know, the kind on guitar cases)...Folding? Just some nice looking hinges. Also, make sure no part of the design interferes with other parts of the design. That's why the simpler the design, usually, the better.