You cannot use DLC objects on non-DLC tracks and vice versa. The game does not even look into the corresponding folder for them, doesn't find them, and then crashes.
You can undo everything you do. When you add random objects, you need to copy over parameters on how they were originally used, as stated in the documentation.
You should look at where the objects are used, my info dump lists the references. I find most names pretty descriptive, most have the japanese name of the object. A thumbnail list is not possible at this moment because it is too slow.
"Getting errors" is unspecific and I can't help with that. Blender keeps a copy of the originally loaded BYAML in memory as long as it runs or you press F8 (which you shouldn't anyway if you're not a developer). This is because some sections are simply not rewritten from scratch and taken from the original file.
About the other stuff, you have to ask the game developers. You can't expect most objects to work just like that, especially if you don't copy over their original parameters. Buses are indeed following a path which can be set but not edited yet. If there is no path, the object probably appears at (0,0,0), invisibly to you.
