As for the last two questions, Peddie is rigorous, as are most top BS, and it requires proper time management skills. The school does a good job of guiding students towards those skills through office hours, formal advisory meetings and mandatory study hall early on.
Workload also depends on class placement and selection. Language, Science and Math classes are leveled in honors/regular, in the case of Math honors/advanced/regular. This ensures that everyone is challenged at the appropriate level.
The culture is overwhelming collaborative, and kids are supportive of each other across the board.
We have had the occasional encounter with a teacher who was not the right fit, but classroom experience has been overwhelmingly positive. There is also the safety net of add-drop period and I have seen intervention at surprising late dates in the rare occasion where the class was truly not the right fit for whatever reason.