stud sizes of terminal boards, matching spade lugs?

Suggest you go to the web sites of the manufacturers of the particular terminal boards you're interested in and download specifications (usually pdf documents) that should give you such info; same with the spade lugs. But generally both would be spec'd for standard screw sizes: numbers (4, 5, 6, 8, ...) in the US and metric (millimeters) pretty much everywhere else. Those of us in the US that manufacture for the international market really are using metric wherever possible, and some day someone with some real leadership will wake up and get us really converted over to metric. Sigh. BTW, you can (or at least used to be able to) get rows of spade lugs on an insulating strip to match particular barrier terminal blocks, both from the same manufacturer.

I think you might benefit from looking through the Keystone Electronics catalog, they have some dimensional drawings.

In the US, #5 or #6 screws are the most common on small barrier terminal strips. Spade lugs are available in #2, #4, #6, #8, #10, 1/4" etc. screw sizes.

Tim.