You need the multi-engine rating to do a ME IR - so your sequence would probably be CPL - MEP - IR. The MEP rating will of course be valid on your CPL.
When renewing the IR every 12 months, you normally renew your MEP rating in the same checkride - I don't know if you can do your IR skill test and MEP skill test in one single test, adding both MEP and IR at the same time.
If you have to go through an approved CPL course, there is an option to do the CPL in a ME and do a single skill test for CPL and ME rating. This saves a few flying hours.
C.