Following thoughts on your questions:
There is no specific difference in preparation process for interviewer or interviewee led cases. Interviewer led cases are used mostly by McKinsey. All other firms use rather interviewee led cases.
Strategy & is former Booz & Co, was acquired 7 years ago by PWC. It is still a "company in a company" with its own corporate culture. Previously MBB was actually MBBB - the top 4 strategic consulting companies also included Booz & Company, as it was a very prestigeous firm.
PWC has a different business model and kind of projects than Strategy &. It's typically an advisory work, while Strategy & does the classic strategy and operations project like McKinsey or BCG.
Strategy & is particularly historically strong in the Middle East. It's ranked 2nd after BCG. The compensation is accordingly way higher than in PWC.
Last months I helped 2 mentees of mine to get offers from Strategy & Dubai each 80k+
Drop me a line if you need help to get yours!