My advice is to do the CPL skills test (and the training before it) before you take on the IR. Also, if you can afford it, do the CPL on a twin as this will give you a leg up on the IR as you are already up to speed on the twin.
Alternatively, do your CPL and IR on a single and only go for the twin later when you need it.
Regardless of which option you choose, I would suggest that you are better off to do the CPL first as handling experience you gain there will make the IR a bit easier.