Bicycles should be required to be sold with a sheet of all the measurements of replacement parts. I find that buying the correct part is often the biggest hurdle in maintaining my bicycles.
Complete bicycle manufacturers usually make these specification lists public in online and print catalogs. Component-level repair, as in many other fields, requires more specialized knowledge and a parts list is rarely practical nor helpful.
I'm happy to learn about it. I've owned trekking/urban bicycles from multiples brands and never found such documents, except maybe using archive.org to get old marketing pages.
OMG yes. This so much.
Or just small details like: If you already provide a list of what rim and spokes, maybe add the size of the spoke nipples. Or what model of brake pad.