If you get the retail of SuSE 10 there are a few differences, as oppsed to the eval and OSS, etc.
1) Yes on all
2) It comes with, so pretty easy, worked right out of the box for me.
3) If you are reffering to
"Hacking OpenSuSE" from the Jem Report : It does apply to all but Retail as I understand it, retail comes with full mp3 support out of the box (anyone can correct me if I am wrong, but I have read that.)
4) Directly in that Jem Report, mplayer, along with full avi, divx, dvd, xvid, and quicktime support, and xine, are all there.
5) If you can live without it normally, I don't see why not. But I haven't tried, I like full Desktop Enviroments.
6) The way I understand it, you do not need SuSE's YAST to do it, no. You can set it up to work in straight command line, as for out of the box or setup... I don't know, I didn't really look into, I like YAST, it is like a security blanket for me not to hose my dependencies and installs.
7) Good luck!