Should I feel bad about putting my two weeks in?

Seems to me it doesn't have to be all or nothing. If you are overwhelmed between school and work, cut back on one or the other. In this case, obviously that's work. Go to your boss, tell him/her what you're up against and ask if your needs can be better accommodated (fewer hours, less responsibility). If not, then go ahead and give your two weeks with no regrets or guilt, knowing that you did your best to make it work.

Not at all. You do have priorities in life, and your boss will respect you for taking care of your priorities first. Plus by giving notice and doing it for a good reason you should be eligible for rehire if and when you are able to work again, and having a leadership position even for short time will look good on a resume.

If the new responsibilities/time commitment is too much for you, nothing wrong with quitting. If you liked your old job before promotion, you could ask if you could return to that pay level with the reduced responsibility.

No, you shouldn't feel bad. You are going to school and you want to focus on that. Working and going to school can be tough for many of us... especially if you're going full time.

Talk to your boss and give them enough time before you quit. And ask them if you can arrange to come back once you take care of your classes. I am sure if you word it correctly, they wouldn't mind letting you go and possibly hire you again if you want.

You gotta do you kid.