Ad 1: It's a precaution I take when I start learning a new system: install it on it's own hardware, or at least in a virtual machine. That way, I can tinker around as much as I want, and even have the system completely unusable, without endangering my main machine. (Some) VMs have the additional advantage of allowing snapshots, so you won't even have to reinstall.
Ad 2:
Wikipedia:
Quote:
[...]Open sourced components are snapshots of the latest Solaris release under development. Sun has announced that future versions of its commercial Solaris operating system will be based on technology from the OpenSolaris project.[...]
Ad 3: As I said, commercial Unices are usually tied to some hardware and support contracts. Software-wise, they aren't made to be cutting-edge, but stable and tested.
Ad 4: You only listed 3 different OS: Linux, Solaris, and BSD
. For the Linux distributions you listed: they are pretty much the same. Fedora is the "staging ground" for Red Hat Enterprise Linux. CentOS is RHEL, without the commercial support, and some commercial extensions cut. Other distributions include SuSE (SuSE Linux Enterprise Server/OpenSuSE), Debian (Ubuntu), Slackware, and Gentoo.
Linux distributions usually have tools for most languages included, and a huge subset of that is available on other platforms (eg. the GNU Compiler Collection [C/C++/Objective-C/Java/FORTRAN/Ada], Perl, Python, Ruby, ...)