You need to have a look at the requirements for the various certififcates you are going for and plan accordingly. The FAA IR requires 50hrs (I think) cross-country flying before you can take the test. The CPL has a minimum number of hours before the test too.
If you talk to a good school they will help you with the most economical route. I used Tailwheels Etc at Winter Haven (now at Lakeland) and they tailored a program for my particular needs - in fact, the primary reason I chose them was because they actually looked at my somewhat unusual experience and worked out what I needed to do. Their IR package was good to - a fixed price for as much flying and ground instruction as you need to complete the IR. I am sure there are other schools out there which will do the same for you.
The route which worked for me was Private then Instrument then Commercial then Multi.
Another t op tip - get all of the exams out of the way (if you can) before going to the US. It means you can just focus on flying and preparing for the test rather than having to do book work while you are there.