What I do is I drill the holes before I start shaping the scales.
That way it is very easy to make sure that the holes are aligned perfectly. Drilling the holes afterwards is possible too, but typically a bit more finicky.

But the scales you made look really nice.
When they are ready, you should coat them with something to make them water repellant.
My personal preference is antiques wax, but you can also use beeswax or something similar.

Some peope also use CA (superglue) or epoxy coating but I don't. I don't like the glossy look. Instead, I prefer that wood feels like wood. But I do coat the insides of my scales with superglue to prevent moisture from seeping in.

Also, have a look at the FAQ / resources sticky of the workshop forum.
it contains lots of links for buying things like pins, washers, 1/16 screws, ...