Now, in the 3 or 4 years I have been messing around with boost, there has been one thing that it came down to every single time...do it right the first time.
MOST people boost the car, drive it for a while, get the boost bug, and then want more, so they spend more money upgrading, and the money sucks...you, on the other hand, already know you are planning on upgrading so my advice to you is this: wait. It sucks, I know, but you will be so much happier if you just wait, save up, and do it right the first time. Upgrading ends up costing so much more in the long run for many reasons...1) You have to get the car retuned each time, 2) The original part you used is now "used" and you have to take a loss on it when selling it, 3) VERY often, you can not only upgrade 1 or 2 parts, there are a few parts that work as a part of a package that will not work as part of another package.
I know you are set on boosting your car, and you should...but wait.
I spent 8 months buying parts for my first setup...I'm on my 3rd or 4th now...