Ubunku vs. SUSE, Gnome vs. KDE

That's becuase Suse was originally a German distribution. It has now been bought by Novell and become much more corporate.

If your Macs are PowerPC-based you'll be limited as to which distros you can use. The newer intel ones are much more compatible with linux.

Not a bad move ;-)

Try a few. Have look on distrowatch.com and pick a couple with a LiveCD, which you can run fully from the CD - no installation required! :-) Then you can try before you buy. Be warned though they will run slower from the CD, so the performance isn't indicative of what it's like from the HD. My personal favourite is Mepis.

The 'enterprise' version of Suse isn't free, but OpenSuse is.

The best version is the oneyouprefer.

Yes and there's also Xfce, ICEwm, enlightenment, etc.

Similar how?

As you're used dealing with different OSes already you should be comfortable in Linux, but be prepared to learn the idiosyncrasies of Linux ;-)

Ubuntu is debianbasedwhich means it does many things in a similar manner to the debian distro, particularly in installing and configuring applications.

There are also Red-Hat and Slackware based distros.

No, Suse isn't debian-based. Debian is an excellent distribution, but is not very newbie friendly which is why there are friendlier versions of it like Ubuntu, Mepis, etc.