hi limotux,
when i did DU in my LMDE-testing install, about one hour ago, all went fine, granted i didn't had any libxine* to mess it, but i presume the way you did it sorted the dependencies errors better than synaptic (sometimes happens, sometimes not

), if you browse through the LMDE breakages thread you'll see a couple examples of this;
about your plan, i think it's amazing

just a couple random ideas:
- i wouldn't go with LMDE-gnome for that plan (although i use it for more than 1 year now, and the new update-packs will make it a very stable system) we can't forget that gnome3 is coming in, and you don't want that change happening in dozen of comp. with noobies in front of them and with important tasks to do;
- the option is LMDE-xfce, if you haven't tried yet, give it a spin; you get basically the same look&feel of the gnome ed. and the same functionality, avoiding the big gnome3 transition;
set those systems to track latest, you will get updates once a month more or less and you can be sure those updates won't be disruptive;
looking forward to hear more from this
