I've seen loads of two person companies with a CEO title. And even single person startups with 0 employees sometimes have a CEO. If I were you, I'd get less hung up on titles and just get to work :P
Agreed. At least with my start-up there were so many roles for each person initially that titles were just there for your reasons. It most likely makes sense later, when roles are more clearly defined.
But titles are free, so if they make you feel better and make you more productive, might as well give yourself one