a.) what (linux) distribution do you use?
Gentoo.
b.) does the distribution that you use supply a lot
of
audio-related packages by default?
Yes, and most of them in relatively recent versions. The rest
can be installed by user contributed ebuilds or by building
them from source.
c.) do you consider the distribution that you use to
be
notably adequate for audio production? why?
With a custom kernel, yes it is. But Gentoo surely isn't a
distro for the beginner. Much settings are done by editing
configuration files. There's no YaST or DrakConf.
Best regards
ce