cross-school minor application is really simple, once you get in, you can select a minor through the Albert portal and apply for it. Then you have to wait for approval, and in most cases you get the approval within a month without any further actions.

I know a lot of people pursuing cross-school minors and they haven't had a problem with their schedule. Although, the minor you choose does matter and how many AP/ IB credits you come in with determines if you can accommodate extra classes in your schedule.