mb2ai
I believe the reason you only get 3 attempts is that the CAA only issue 3 exam papers for each subject, and therefore to retake a 4th time you will be doing a paper you have already failed. There is no guarentee they will let you do this, so don't rely on it.
The best study technique I can offer is to plan your subject order well. There is a lot of overlap across the subjects, and things make a lot more sense in a better order. For example, I found nav a lot easier having already done met.
I spent about a week learning each subject and got first time passes on all. Highest was 100% on HPL, lowest 75% on met.
Use the PPL confuser, it's brilliant.
Good luck to all.