I'm not sure what you mean by counting MEP time as being PIC while getting your IR, but the answer is no. You can't count time as PIC while you are being instructed because your instructor is the PIC. But I don't see why that would be a problem? If your TT is 150 hours, I would say that you already have 100 PIC hours??
As for the other question I would suggest that you take this route:
-ATPL theory
-CPL first (you can do it before reaching 200 hours, but it will be issued when you reach the 200 hours with 100 PIC hours and some other requirements)
-IR/ME
When you finish this you will have your Frozen ATPL. Do a MCC after this if you would like to apply for an airline job.