RE: Nude references - I have those. It's a reference for the character's exact proportions under their clothes. My first comic I didn't do that and I suffered a lot because my character kept changing sizes between panels since I only had a reference of him in his common outfit, i.e. a bulky over-sized sweater (and in those panels he wasn't yet wearing it).
IMO if you're an artist/writer all-in-one-combo deal, then the best reference sheet is the one that covers your weaknesses - everything else is a waste of time (i.e. time you should be spending on your pages instead, lol). Mine is proportions, so I just have that, plus just really old art and sketches that still contain the bits of character I'm using. I used to do expression/head references as well, but then I realized wait I'm actually not bad at winging those, so I stopped. I wing the alternative outfits as well.
If you're for whatever reason working as part of a team, then you need the whole kit and caboodle. Front, 3/4, side, back whole body; head and expressions + alt outfits (to portray the character's personality); nude figure (again, for proportions); close-ups of any details (both front and from 3/4+ the side, if they're 3D details).