Here are a few more comments on your points:
(1) Internal storage means, among other things, that the user can only access it with a rooted device.
The path to the appPackage and the private data dir is:
/data/data/...
/data/user/0/...
The path to the external storage is:
/storage/emulated/0/...
where /storage/emulated/0/ is the root directory of the external storage.
The right understanding of internal and external storage is fundamental for any work with Android.
(2) The private storage is in the internal storage and, as far as the ASD is concerned, in the external storage. What's hard to understand about that? Both will be deleted when the app is uninstalled.
(3) No, I just haven't bothered to remove those lines from the original. But the above part should complement and explain the logic of the whole storage system.
(4) That is described precisely. There are some shared folders that act as shared storage and are reserved for certain file types. What is unclear about that? Basically, that is what Scope Storage Stuff is all about.
But I like to admit that this scoped storage stuff is confusing, see also here.
That's why I created this overview.