DLL Import problems - "Not found" & Proper setup?

I have a .dll that I build from a cpp library in visual studio. I have placed it into the Plugins folder in my assets directory, and I have a .cs importing the externalized functions. I've gone over this issue a couple times now in the past month with different libraries, and in the past all I could manage to do was have the plugin load properly after a build. Whenever I've tried testing it in the editor, it gives me the "Dll Not Found" error.

My main questions are these:

Why can't I use the .dll in the editor, but I can use it when built?

Is there a guide to the proper set up of a plugin that goes into more depth than the Unity documentation? (ie. are there any weird naming quirks? special build settings? so on)

One strong example of the "little quirks" that I'm looking for is that on MacOSX, I was able to build a cpp based bundle that worked in the Editor and in an executable, but only if it was built on the Carbon framework, not the Cocoa framework. There was no indication of this necessary setting, and I only found it by chance.