Wasn't sure where to post this, as it's kinda CS related, but you can't do this in the CS, but there might be a tool.

Is it possible to display NPCs with all their gear and their animation file, just like if you preview creatures in the CS or NifSkope. Would be really handy.

It's not quite what you ask for, but http://www.angelfire.com/rpg2/mad_weather/animexp.htm is a small mod allowing you to see how various animations look in-game. Be warned that various animations may be mapped differently in Morrowind-only and Tribunal/Bloodmoon-based games and not match their titles; it is a bug of Morrowind engine, not of the mod itself. You may edit it to give test NPCS necessary race and gear (or make them companions and change their gear just in-game; this is something I didn't think about when making it).