I followed the same trend giving exam 4 first, then 3, then 1, then 2. However, if I could change that order, I would. You will surely pass exam 4, however once you pass, your 2 years time limit to pass the other 3 starts and exam 1 & exam 3 needs at least a month or two to prepare (maybe more). I would start with one of them, and if you pass it, you will surely meet the 2 year deadline. With the new 2019 syllabus, all might change though