Depends on your concentration. My BSE son is studying ORFE and is studying 4-5 hours a day, including weekends.
Difficult with BSE, little less with AB. Son earned a high school 4.0 (mostly all AP student) getting a 3.5 with intense studying and taking 5 classes per semester. Son was an 36 ACT excellent student.
No
Pretty hard. If you try at all you can earn a C.
Collaborative at Princeton.
Fairly stressful, but taking 5 classes for BSE. AB's four classes would be less stressful.
Much harder to get in. For BSE classes easy to get a C, hard to get a B, extremely difficult to get an A.
Cannot compare, but if you examine grade distributions at Harvard vs. Princeton (look up gradeinflation website) you'll see Princeton average is lower than Harvard, Yale and Stanford. If medical student this might be a concern, otherwise don't worry about it.
Any of the schools listed will be difficult. Where do you want to be next 4 years? What do you want to study? These are the important questions…