If the Ardour package doesn't work out of the box, I think the
place
to start is filing a bug (or bugs) against it.
I'm no expert on PulseAudio (my only advice is that in Xfce, you
MUST
install
https://apps.fedoraproject.org/packages/pavucontrol), and I
know nothing about Jack, but I bet there are plenty of Fedora users
out there who have experience and tips to share on Ardour.
Ardour itself is working fine.
What I'm trying to do is, at least, raise awareness about bad
out-of-the-box integration between PulseAudio and JACK in Fedora
Workstation.
Anyway, thanks for the tips :)