Well, when I pick one, I look mainly at my body type and cost-friendliness xDD And of course my favorite character.
Though unless your character has something like their midriff showing, you really should let that stop you =D
For hair color, there's wigs... Eye color, there are contacts... (even though people won't really care much for the eyes if you put a lot of effort into your outfit ;P) And a little makeup can help, too =o
You shouldn't really put any restrictions on who you want to cosplay. Just do what you want! It's all about having fun after all, right? x3
I used to have a ton of great articles on cosplay discussion and help, buuuut.... Firfox kept deleting my bookmarks D:
Be sure to note, cosplay is a learning experience!! >DDD Or something. Well, it is DD: likelike... math in the sewing... and craftwork... and science if you want to do certain effing hard things like foldable/flabbable wings owo; Andand... There's history in it somewhere... right? RIGHT???
*scurries off into corner*
And if anyone says it's stupid and borders on obsession, just bring up the whole fact that people do similar things for sports teams and such >3>