Your options are very wide and complex if its about learning sound engineering. My first question would ask: You are wanting to set up a studio to learn about what? Home recording or an actual studio?
You could start with a preamp/channel strip combo or more likely get a converter with pre's build in.
What about the room, sound treatment, monitoring?
this sounds like its a question on a test for an audio course.
first we need a definition of what "all good studios" means ???? also what is a "mid to high" budget?
if you mean a major recording studio with an LFC and large recording spaces for orchestras or is it a studio for tracking POP music? the requirements are very different. didn't your instructor already go through this with you?