Your ability to take major courses is going to be quite limited in Fall Quarter. CMSC 121 falls under the Core Curriculum (Mathematical Sciences), so you might be able to register for that. Here’s a description from the college catalog:
"CMSC 12100-12200. Computer Science with Applications I-II.
This three-quarter sequence teaches computational thinking and skills to students who are majoring in the sciences, mathematics, and economics, etc. Lectures cover topics in (1) programming, such as recursion, abstract data types, and processing data; (2) computer science, such as clustering methods, event-driven simulation, and theory of computation; and to a lesser extent (3) numerical computation, such as approximating functions and their derivatives and integrals, solving systems of linear equations, and simple Monte Carlo techniques."
http://collegecatalog.uchicago.edu/thecollege/mathematicalsciencescore/
Could be wrong but I suspect that BUSF 30000 will be off limits to incoming students.
You will receive detailed information and advice over the summer and Summer Advising will be on hand to answer any questions pertaining to registration. Two years ago, it seemed that the big decisions for my kid were whether to take a fourth course in the fall and, if so, should it be foreign language or PhSc. She already knew she would take Sosc., Calc. and Hum. (Hum required at least two quarters your first year and you are automatically re-enrolled in the Winter).
Here is the Curriculum section of the College Catalog to get you started on perusing prospective courses. Sequences do tend to be strict, although some of the Civ can be taken out of sequence.
http://collegecatalog.uchicago.edu/thecollege/thecurriculum/
The College recommends that you complete the Core by end of 2nd year and gives priority in registration to the lower grades (rumor is that you can’t get in to Core Arts as a fourth year, for insance). Some with a heavy STEM load and/or who are doing their Civ as a study abroad might put it off till 3rd year. All first years take at least two Hum and the large majority of of the class will have completed the three quarter Sosc. sequence by end of 2nd year.
This will depend on AP credits brought in, but the basic Core requirement is at least 2 each of Hum and Civ, and at least one Arts; at least 2 each of Bio and PhySci and at least one Math. 3 Sosc (in sequence). Fulfillment of the F/L requirement is towards the bolltom of that curriculum link above.
Here is the description on testing out of certain requirements/brining in outside credit (such as AP/IB).
http://collegecatalog.uchicago.edu/thecollege/thecurriculum/