I've read a lot, tried a lot of things. It always seems to end up messy and somewhat confusing.
I finally tried something very simple, and it seemed to work well for me.
The result is a small number of files which I understand, and are easy to locate. Everything works as expected.
I suppose I could take advantage of more items from Standard Assets, maybe one by one? Importing "everything" seems to create a jungle, compiler warnings, dependency issues ...
So you're trying to use the third person controller from the characters package? There's a somewhat easy way to get just what you need from the package. First import the entire package. Next select the third person controller prefab, right click on it and "select dependencies". This will highlight all the files needed for that prefab to work correctly. With those files highlighted still, export the package. You'll see the export window popup, from there deselect "include dependencies", since you already have all the dependencies selected you don't need this again. When you deselect that it should display only the files that are highlighted to be exported out. Then you can click "export".
There you go, now you have a Unity package that contains everything you need for the third person controller and none of the extras. Using the Unity packages can sometimes be a bit of a pain since they usually come with fairly large packages and Unity loves to have multiple scripts dependent on each other at times.