As noted by W-EI, you need to check two Code sections. Art 450 will help you size the protection for the transformer itself (you can follow the chart for maximum primary and secondary protection). Once you have selected your protection, check 310.16 for ampacities and 240.21(C) for conductor protection. A lot of folks get confused between the two, but Art 450 is for transformer protection and 240 for conductor protection and you must consider both.
You mentioned a primary disconnect. You are not required to have a primary disconnect for a transformer. Your OCP device for you primary branch circuit can be your transformer disconnect and it can be located anywhere (in the same building)
At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.