I'm not sure how I can prepare for stage 4. Any suggestions?
Take a look at another thread, "Advanced Flight Grading". Hope it gives you an idea of what to expect. Try your best and don't panic, while it is true that more and more people are failing FG, I'd say it is simply because there are more applicants nowadays than before. As long as you can show them your learning ability, you should be fine. Good luck!