New here, Distro suggestions?

[CrocoDuck]

The manual say's:
"Official packages of Mixxx are only offered for Ubuntu Linux."(at 2.3)

Just let me clarify this further. Software written for Linux will run on any distro. The Mixxx developers are not developing for Ubuntu only (actually, I don't even know how one could go around developing something for a distro only). However, when it comes to distribute pre-built packages, they decided to distribute pre-compiled packages (not the software itself) for Ubuntu only, even though the software can run probably even on not Linux OSes, like FreeBSD. This because they want to maintain just a single .deb package instead of many packages for every package manager of every distro out of there. This means that if you are not on Ubuntu you have to either: build Mixxx from source or check whether your distro maintainers are themselves maintaining a package. For example, Arch Linux package maintainers maintain a Mixxx package in the repos.

About distros and documentation, I wrote about it in my Blog:

Pro Audio Linux Distributions
Pro Audio Linux Documentation

[CrocoDuck]

Perhaps something for the future? (although i've tried some other distro's, where my most satisfaction stayed with ubuntu then).

Well, as long as you are happy with Ubuntu I don't see why you should search for something else .

... even though the software [Mixxx] can run probably even on not Linux OSes, like FreeBSD.

In fact, there is a FreeBSD port for it. At a very ancient version tho.