Are you planning on getting an IR (H) as well or something? If you only want an IR (A) you should just do the ATPL (A) exams. If you do ATPL (H) first, you'll still need to do an additional 5 bridging exams.
Either way, get your IR via the IRR and CBIR route - before the CPL. And don't believe any flight school that tells you you need an MEP rating!