What are the steps for further education if one has there undergrad in Marketing/Business, but not education? What sort of degree or certificates would you need to become a high school business teacher?

I’m not familiar with other state requirements, but you can prove subject matter competency in California through the CSET exams — that’s proving your qualification to teach Business. In terms of acquiring your teaching credential, you need to take and pass the CBEST exam (an English/Math basic knowledge test), and you do need teacher credential courses (usually 1 – 2 years) to earn a preliminary credential.

Again, in -California-, demonstrating subject matter competency, passing the CBEST, and completing a teacher credentialing program will allow you to get a teaching job. For other states, you can probably find detailed requirements at their state department of education websites. Good luck.