To create a material that is wireframe only just tick the checkbox. This should be applied the same way, as a replacement material which you can apply on the individual meshes when needed, and later you can just revert back to the original materials. Dynamic material instances will help you doing this.
Well that’s a bit tricky and i’m not sure what could be an efficient way to implement this. Pry the material LODs would help but it’s not a thing just yet.
It’s good, then you must understand that this shader art is a form of art that do the styling with decent understanding of mathematics (and shader coding as well), and usually you end up creating only the illusion of (imitate) something that you have originally planned to do, which takes time to figure out! Just don’t rush ahead. The web is full of great articles explaining how and what can be achieved, and where the boundaries step in (which usually gets expanded by the talented ones), and it takes some time and learning (and patience) to get to it. Similarly, to learn the proper usage of the pen while you’re drawing your first things on a paper.