From someone who went to different colleges my advise is to take no more than 15 units your first quarter as it is difficult to adjust to a new environment. You will be going from knowing your professors well, having near one on one office hours. having small classes, and you might have had extra credit in CC to boost your grades. However, at UCLA you won't have any of those benefits, so it won't be as easy to adjust, so I don't recommend getting ambitious and taking 18-21 units till you feel you can handle the load. From my experience you might be working just as hard to get A's with 19 units at CC as 13 units at UCLA, competition is a lot tougher especially in science courses