If your looking at doing ATPL's and IREX as well leave CPL human factors for last then sit AHUF the next day, MET too except there is some new content to learn. Do CPL law then IREX then ALAW as the former two make up alot of that exams content. Basicly if you can do them all without big gaps between exams you will find the journey much easier.
Many seem to recomend that you do CPL systems then CPL aerody, as it helps to know how it works before you start looking at how it works from an aerodynamic perspective.
Get into them, stay at it and they will be over before you know it. Good Luck!
