1.) Yes. Only 75% of the PMP exam is based on concepts that come from the PMBOK Guide. These "applied concepts" interviews introduce you to additional concepts that may show up on your exam.
2.) HR Theory part 1
3. You have to go through them with the same diligence that you apply to all the other study materials.
Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®