You also need to learn what deraileur specifications to pay attention to. Here is a link to one site that will help you understand them. It's a site for Di2 and electronic shifting, but the same thing applies to cable pulled DR's.
https://bettershifting.com/installat...pecifications/
There are probably other sites that explain it better, but this will get you started so you know at least what kind of questions to be asking and what terms to search on.
The
Shimano website will have the spec's listed with all their current products and the specs and compatibilities and all sorts of other information can be found at their documentation website.
https://si.shimano.com