Quarter system does allow you to take (or sample) more courses, but if you annualize/normalize them, their requirements, ease of scheduling, etc. tend to be about the same. Open curriculum obviously gives you more flexibility. However, I’m not sure either has anything to do with interdisciplinary studies.
The areas you’re interested in are highly connected. CS spans a wide spectrum. Math is integral to a significant part of that spectrum. Some of it requires more abstract math and some of it requires more applied math. Interactions between the two are common and expected on most campuses. There’re some interdisciplinary majors (e.g. CS+X) that some colleges offer, but I don’t think you’d be interested in those.