I was wrong, I just looked and a 200 MTOW is exactly 12.5. But anyway, I personally do not know the reason some aircraft are certified single pilot.
As far as school goes, it has been tough. Fortunately, I have not had to miss too many classes to go fly trips. I have Tues/Thurs classes. I spent a week in Florida for training on the King Air and it was tough to get caught up in my course work. Me being in school was of concern to my now current employer, but I assured him that my schooling would never interfere with his flight program.