Yeah svt pump is good fora bit, thats what i have and in a few years will prop dump it when i work on the build some more. To change from 8 -10 psi you just need to purchase a pulley from Procharger. Get it tuned right away.
High miles id stay away from 10 psi but 8 psi and a good tune is def fun. I'm pretty sure you have an intake pump, thats what mine was, its not to hard to change just make sure before you do it you drive most the gas out.
start off with the 8 psi setup then go from there. when you see people talking about the 400 whp max number, they are talking about through a manual tranny. Manual tranny's have a lower drivetrain loss than autos do. its somewhere around 13% loss on a manual but closer to 20% loss on an auto. So 400 whp on a manual that would be about 450 crank hp...450 crank hp would be around 360 whp on an auto.
As for the fuel pump, its pretty straight forward on replacing it. Don't remember if you have to splice into the wiring or not...kind of think you dont, correct? One thing that you definately should NOT do is drill holes close to the bottom of the basket...that is a cheap bandaid fix that can cause serious problems.
for 8 psi the svt focus pump will meet your needs. if you want to start messing with higher amounts of boost go with a ford gt pump...or even better yet get a dual pump cobra tank (but thats an intensive mod)