don't be afraid of taking classes.
people who advise you not to take more than 4 courses first semester are people who are afraid of working, probably students who have never had a high university workload, and are just a bunch of bull anyways. university is a big adjustment, and classes are part of it.
take this coming from a guy who had 7 courses consistently through university. engineering courses. take as many classes as you want and feel you can safely take. experiment. have fun. i can't stand arts or social science students who had 15 or 20 hours of class a week who complain that their course load is too high. it may not be the easiest, but a 33 hour/week classs and lab schedule in university with hard engineering courses didn't kill me and wasn't unfairly taxing.
if you're allowed to and need the courses anyway, sign up. if it seems too stressful, then drop a course off the bat and take it later. it's not a big deal. sign up for non music courses too, and if you can handle them and get something out of em, then you will be better because of it, even if it is more work than most people would advise.
just keep your head on, don't get overwhealmed, and experiment. if it seems too hard, then lighten up the load. if you think you can take on more, which you probably can (if you don't listen to too many music majors telling you not to do so your first couple of days), then try it out. the worst that can happen - well, it's probably not too bad at all, so just go for it.