First off, let’s agree that namespace should match folder structure and that each language artefact should be in its own file.
(see Should the folders in a solution ma
I prefer a flat structure with projects in the root.
Inside of these I have various folders and namespaces. I only create different assemblies for deployable units. Small apps won't even have this amount of separation. IMO this keeps things simple. If I ever decide that code I have needs to be used elsewhere, it's easy enough to break it into an assembly if needed, as long as I've followed good namespacing practices.