I've got the CX Racing kit sitting in a box waiting to go on my Paxton when I get the new motor in. Its a good looking kit.
Intercooled I would keep the boost to about 10 psi, non-intercooled 6-8 to be safe.
You will need a new tune for a new pulley yeah... and the intercooler as well. If you change pretty much anything on the motor/blower for a car like that just assume you need a tune.
So first, calculate out your pulley sizes and how much "boost" you actually will be seeing. Run everything by a good tuner and see what he/she says and recommends and go from there. Honestly you should be talking to your tuner about this FIRST.
Blower cams could not hurt either if you have the coin, that is what I am doing on my stock replacement motor even with its stock internals. I will be able to get the max power my internals can take out of way less boost which is easier on everything and a much better powerband as well. Plus that choppy idle you can't get on the newer 4V cars...
One other question... what sort of suspension work do you have done to your car? If you are stock suspension or just lowered with some control arms you will see a MUCH better gain in performance by getting a correct suspension setup installed/dialed in than just trying to squeeze a little more out of an already stressed engine.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.