Jesus dude, calm down
1.You don't need disc's on the rear, only for cosmetic reason's (big alloys so you can see the disc's)
2.I got one of them boxes off ebay, wow what a difference. (Normally range from £70 to £400)
Tune it box £54 (make sure you have the right injector pump to fit this one though) max. + 38 BHP and 70NM torque maybe)
Tune it box £80 (upto +30bhp 50Nm of torque)
Tune it box £395 (116-132 bhp 253-276Nm of torque)
3.You won't need to run a larger intercooler, but if you want to apparently one from a Vauxhall Movano or Renault Traffic will fit behind the front bumper(Don't take my word for it though)
4.Don't know if any banded steels going, why not get some made up from spacesavers?
5.If you ever want to change the exhaust, you only need to run one box, but apparently you can run it with NO box.
Replace the standard air filter with a K&N one (not a cone, as this will reduce your torque) but they do sound great