Hey there! Current M4 here as well, free to answer any questions anyone has in my DM's!
1.) Exams are in house, but modeled after the NBME "style". They follow the same structure as NBME exams and have been vetted internally so as to reduce any bias in the questions. Exams were more than fair and I can tell you as someone who got straight B's/2 C's in med school, it did not affect my match whatsoever!
2.) Some classes are P/F. Your P1/P2 (practice of medicine) modules where you learn all your clinical skills is P/F, the C1 module which is psyhcosocial issues in healthcare is P/F. Most of the science modules if not all are graded A/B/C/F, only during my first year (during covid) were some of the science modules P/F. Again grading is irrelevant and if you want an A you will be able to get 1, they don't gate keep A's.
3.) There is usually 1 exam for each module, apart from the first module (biochem/genetics) and the second (anatomy/phys/embryo/histo). Those ones have midterms that are graded. The other modules that have 1 exam, usually have a formative exam (doesnt count for anything apart from seeing where you are at) halfway through. Theres also formative quizzes weekly to cover that weeks material for most of the modules, and some modules will have biweekly or weekly quizzes that are worth a small portion of points. In general most have 1 large final exam but it doesn't usually dictate your whole grade, there is plenty of buffer points through some small assignments/quizzes.
Again happy to try and answer any questions ya'll have though I am a bit far removed from the first 2 years.