Structured case's main challenge typically lies within the need to shift through the provided materials in an efficient manner (15+ pages, going as high as 30-40 in some cases) and identify the most important data which provided answers to the questions at hand.
The tricky part is sometimes, the important data is located on the footnotes instead of the main graph or content of the slide pages.
Hence, attention to details while being able to rapidly looking through the materials is crucial.
Different from unstructured case, there is less of a need to estimate the data through market sizing approach as most of information are contained within the booklet.
It tested the situation every consultant faced during the early hours of entering a new project, where one is provided with bucket loads of information on a new industry or function and they have to 'get up to speed' quickly.
Practicing with some casebooks examples from business schools would be useful in getting used to such practices. Try to look at examples of consultant slides online as well and try to simulate asking and answering specific questions from the slide bundles.
As for the second question, the fit part typically contains questions about leadership and conflict management experience in addition to personal behavioral inquiries.
The SCR (Situation - Complication - Resolution) / STAR approach generally works well to answer these.
Hope it helps.