Big 3 will do Econ though then join the business clubs. Or they do the strategy major in the business school.
For business, here are your pre reqs based on major:
https://marriottschool.byu.edu/advisement/applying/prerequisites/
There are some prereqs that apply to all majors. Take accounting 200 before finance 201 is my only advice. But if it’s his first year then I’d take generals year 1, then take prereqs year 2 apply for business school major summer of year 2 and begin the program year 3.
That way he gets a year under his belt before taking the prereqs. However it doesn’t really matter as the prereqs were easier for me than general classes because I hated general classes and enjoyed the business ones.