5) Not really 100% Debian related, but in the Python sdist,... should that contain the debian/*?No, and the upstream source shouldn't contain debian/ anyway, as the life cycles of packaging and upstream sources should be separate even if the person doing both is the same.
This would then be a "native" package, and it's not recommended to use this package format in most cases:
https://www.debian.org/doc/manuals/debmake-doc/ch05.en.html#nativeWhile it can happen that a developer maintains the Debian packages for their own software, they also have to consider other dpkg-based distributions, such as Ubuntu. Maintaining the Debian changelog for both in the same upstream repository isn't a lot of fun.