Actually you don't need to have a CPL for the IR. Current requirements are:
Hold a current JAR PPL or CPL
• Have passed the theoretical knowledge examinations for IR(A) or ATPL(A) in any JAA member state
• Be fluent in the English language
• Hold a JAR Class I Medical Certificate, or Class II Medical Certificate with Class I audiogram testing for holders of a JAR PPL
• Have at least 50 hours experience cross country
I did my IR after completing my ATPLs then did my CPL after that. There are different views about pros and cons of doing it this way. On the plus side you get a 10 hour reduction off minimum training for CPL, the downside you have an extra 5 hours to do for your IR. So... IR first saves you 5 hours ($), and you won't struggle with the instrument flying part of the CPL test.
Conversely there is an argument that having the CPL flying experience first will help you with your IR flying. Probably true to a degree but I passed both CPL and IR at the first attempt so didn't make much of a difference for me.
You'll end up putting your IR onto your CPL anyway so I don't think the order is that important. Any other questions don't hesitate to ask. Enjoy! (Oh and expedite's advice about FI rating I agree with!)