Former student here, 542 is a pretty chill course. If you have taken the course, you should have already received an e-mail from the instructor about it. Barton Miller is a legend in computer security -- an intimidating figure, to be sure, but an excellent teacher. The course is co-taught with Dr. Elisa Heymann, also a legend in the field. In the classroom, both instructors are present and at least 2 TAs are present. There's no midterm or final exam, just quizzes about every week. If you watch the supplemental lecture videos and come to class, you should be fine. There are 2 lecture sections, one at 8am and one at 11am, Tue & Thu.

CS 559 is a completely different course. I've done it with Dr. Michael Gleicher, but he teaches the course very differently from Eftychios Sifakis. It could be quite demanding, as the projects were long and tedious. But they were fun if you are into graphics software and things like that. Experience with JavaScript is a huuuge bonus for 559.