The requirements for a CPL are that, before you start the course, you must have 150 hours. After completing the course, and before sending the paperwork off and applying for the license, you must have 200 hours, including 100 hours P1 time. (There's also a requirement for a 300nm cross country, including stops at two airports away from the airport of departure.) Details of all this are in LASORS.
The biggest problem I see with your original plan is that you won't be getting any P1 time. You will need to spend some time hour-building to get this.
The most common way of getting the FI rating is to do it either after the CPL, or else after the IR.
If you are planning on instructing, then it may also be worth leaving the multi-engine rating and the IR for a little while. They cost a lot of money to keep current - teaching PPL students will not keep you current in either of them, and you will have to spend a few hundred quid every year to get a bit of practice in order to renew them. Remember, though, that you must get the IR within 3 years of completing the exams, or the exam credits lapse.
Hope that helps,
FFF
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