Your looking at a 3-5 psi gain in boost. My opinion is swap the lower pulley first and then do the upper pulley based on the fact it's easier to swap out the upper to achieve the desired boost level. Depending on your mods you can see a 30-75hp increase
As in hardware you mean crank bolt? Stock one works just fine and belt size depends on the size of your upper pulley. I'm selling just the balancer like IW does
Ford recommends using a new Bolt as they are TTY (one use) bolts. IIRC the stock bolt is a M12X1.5X85mm. ARP also sells one that is reusable. I would double check with IW to see if they require a longer bolt. I do not think so on the 5.4 but the 4.6 does. ARP is the way to go. You never think you will have it off again until you do lol.