For the down pipe you will get better response most likely if you post it in the FI section.
for the exhaust, you will either want to go full custom 3" taking every bit of straight section up with resonator. Borla most people like has good over all sound. Flowmaster gives the focus an aggressive idle sound. Magnaflow is in my view the budget version of Borla with a slightly not as good of sound. either way you going to want a long resonator taking up the great bit of straight pipe real-estate that we have.
2001 ZX3 2.0L Zetec-
Hatch Nation #42
Going through Rebuild See "The TICK Build Thread" for details (http://www.focusfanatics.com/forum/showthread.php?t=289168&referrerid=62897)