Don't know where you are going to be doing the CPL course, but it should be quite easy to visit the school and talk to one of the instructors. If that is not possible, speak to them on the telephone. You could also book a one hour flight with them now, and get them to suggest what you should be practicing.
They may well have some notes on the navigation techniques they teach. Like many things in flying, there are often alternative ways of getting the same result.
If the budget allows, you could do the IR first as suggested. I did the IR first but for different reasons. This meant that I could reduce the CPL course to 15 hours, but if I recall correctly, I still needed about 20 hours to get to the required standard.
Good luck and enjoy the course.