2. Bumping debhelper compatibility level, I've chosen to test
new feature to use b-depends: debhelper-compat (= 11) without a
debian/compat file. It you insist on the old way
(I know no arguments agains the new one), it can be easily
changed.
Doing this becomes a problem if you want to backport a package, I've read somewhere that this is not supported on backported packages and you still have to use the old way. I don't have time to go after the url where I've read that right now (maybe it was on the email that this was announced), but there's a chance that's only gonna be a problem until we release Buster.
Anyway that is not a problem as long as you're aware that you have to roll it back for backports, at least for now.
Regards,