Answer#1: Basically I work on multiple characters at the same time when sketching and drawing line art or B/W art, but when coloring I do either. When I'm doing quick "colored sketches" of watercolor with few layers(like this (http://pics.livejournal.com/yumekutteikt/pic/000ats98/)), I paint body parts of multiple characters concurrently(like, the skins of all characters in one layer, then the hairs of all characters, etc); when coloring with dry media paint, I create layer sets for each character and finish character by character, even when those characters share the similar color schemes(like this one (http://pics.livejournal.com/yumekutteikt/pic/0006xs0a/g31)). I dunno, I'm still working to find the best procedure for me.^^;
Oh, and who to work on first? No particular reason, but I start with the one nearest, or if there is no close-up person, from left to right.

Answer#2: Awww, no particular preference in Draco's hairdo unless it's too short. I've seen(and drawn) variety of Draco's hairstyle and still can't pick up the best in my mind. However, the easiest hairstyle to draw is the one in above icon!:-D