So the answer to which activities are mandatory is somewhat complicated lol. Youll have mandatory in person labs almost every week which are OMM, CMR and anatomy (first year). Youll spend an average of 4 hours for each per week in lab (so about 12 total). CMR is clinical medicine and reasoning which is essentially your "doctoring" class. Youll learn how to take histories, do physicals, put a stethescope on the right way etc etc.
You occasionally have mandatory in person lectures but the vast majority of lectures are either live zoom or prerecorded lectures. Most of the live zoom lectures are recorded so you can come back and view them at a later date. Some live zoom lectures must be attended at the time they are delivered. In my experience most classmates will watch pre recorded lectures and zoom recordings at 1.5-2x speed so that they can spend more time on active learning (anki, practice questions etc)
Rotations I don't know much about since I'm a first year. I do know that they have some longitudinal sites in Ventura and Kern County where you do all your core rotations of 3rd year so you only have to relocate once during third year. The other sites are sprinkled throughout the state, obviously focusing on the area around Pomona. You'll be at different clinics/hospitals for each rotation if youre not at a longitudinal site. I wouldnt worry too much about rotations yet, WesternU is very well established so they have plenty of good sites to choose from.