1. All national Authorities are required to generate their exams from the EASA CQB. Some do it by running an algorithm across the entire CQB for that subject getting x questions to meet that LO, y questions to meet another, etc. If they do that the result will be that nearly every student gets a different exam, as the pool of available questions is large. Others take a sample of questions per subject from the CQB, presumably run a validation exercise at national level (so they are not embarrassed by really bad questions) then select their questions from this smaller local database for a period. if they do that the all students will get similar exams in each subject for a period, and the same questions will keep coming up. I think the UK CAA do the latter, hence the last 160/200/300 comments you quote.
2. Only works if they have learned the base material. Three months sounds like overkill, 4 weeks per module should kill it, particularly if they have been exposed to exam questions in the learning phase.
3. In the UK - no difference. If you go outside the Uk see point 1 above.