Yes the questions on airquiz do repeat but you'll probably find the same if you use The PPL Confuser book to practice for the exams. Once you've tried a test once, unless you suffer bouts amnesia, you're likely to remember the questions you have seen before. Best to study until you feel confident that you would probably pass the real exam then use the practice exam to find out if you have left anything out during your study or are weak in particular areas.
The details of the real exams:
Air law and Operational Procedures: 60 minutes and 40 questions
Meteorology: 60 minutes and 20 questions
Navigation: 90 minutes and 25 questions
Aircraft General: 90 minutes and 50 questions
Flight Performance and Planning: 60 minutes and 20 questions
Human Performance and Limitations: 30 minutes and 20 questions
Communications: 40 minutes and 30 questions
Unfortunately I am not really able to comment on the FAA materials being only a humble PPL student myself. Obviously the scientific aspects of aviation are the same the world over and so is flying technique. If the FAA material covers things like flying technique, human performance and limitations, meteorology, and aircraft general then you can probably study from them. Where I think it would differ would be in air law and operational procedures as well as communications to some extent.
All the best
splatt