Yes, Remus is definitely an extrovert. (I'm less convinced that quiet extroverts are rare - I think people commonly mistake loudness for extroversion just like they mistake shyness for introversion, but they're not the same things at all.) I've gone back and forth on Sirius, because his withdrawn behaviour in canon often seems the result of his mental health issues more than a sign he really enjoys being alone, but the fact that he chose to live alone at 17 rather than stay any longer with the Potters suggests a preference for decent amounts of alone time.