1. As I recall, RB uses mainly interviewee-led cases. In London a few years ago I also recall that Market sizing was part of the first round interviews, but this may have changed.
2. At the core, the criteria that all major consultancies look for in candidates are the same. McKinsey's website has a good overview of the "what we look for" part. If you want to get a glimpse into the actual types of questions typically asked at RB interviews, Glassdoor is usually pretty accurate: https://www.glassdoor.de/Vorstellungsgespr%C3%A4ch/Roland-Berger-Fragen-im-Vorstellungsgespr%C3%A4ch-E35272.htm?countryRedirect=true
3. Have a strong answer for "why Roland Berger". Similar to above, go through glassdoor not just for insights into the types of cases that are commonly asked.