If they are included, the packaging repository should have a branch
with upstream files only, and a branch with upstream+debian. The
upstream branch can be tarball imports (one commit per release) or a
clone of the upstream repository (detailed history).
(And yes, it is a known issue that having so many choices can be
confusing, particularly to beginners.)
The git-buildpackage tool can help you with this.
if I am willing to be the maintainer of my own packages, do I still
need to find a package sponsor (given I am not a maintainer yet)?
Yes: the access levels are
sponsored maintainer (named in Maintainer: or Uploader: of a
debian/control but can't upload)
->
Debian Maintainer (can upload their own packages)
->
Debian Developer (can upload any package, including as a sponsor)
https://wiki.debian.org/DebianMaintainer
from the above link, one of the paths is to "Join a packaging team",
for example, how do I "join" debian-science or DebianMed?
https://salsa.debian.org/groups/science-team/-/group_members/request_access
4. submit an ITP bug
Where possible, this should be the first step; otherwise correct.
sorry, forgive me for asking these basic questions.
It's arguably a bug that this information is so hard to find.