HR200
You can start a correspondence course now whilst you are hour building. As long as you have 150 hours just as you are about to start your CPL course, then that would be good timing.
I did my correspondence with Bristol Ground School.
I would also advise you to get your night rating done this winter as it was a problem for me trying to get mine done in the summer of 2005. Get it done as early as possible and then its out of the way.
By the time you have done this and the Bristol Ground School stuff followed by the exams, you will be 18 months down the line and not far off the 150 hours needed for you CPL course to commence.
If you are short of the 150 hours, you could use the last few hours fine tuning your flying in preparation for your CPL course.
Good luck
Rob