Doing the IMC was a big help to me when I started on my IR. As suggested above, I explained to my instructor that I would go on to do the IR and he put me through my paces. It paid off for me and I hit the ground running when I started and I felt like I was ahead of the game.
You need 150 hours TT with 70 P1 to start the CPL and 200 hours TT with 100 P1 to claim the CPL. Note the 30 hour P1 gap as there is no P1 time on the CPL course (except the P1S you can log for the test if you pass). If you start with only 70 P1 you will have to hour build before you can claim your licence.
Once you have the CPL you can reduce the IR by 5 hours to 50 hours.
Good luck.
NH