Well you just happen to be in luck because I just got finished doing the tiburon brake swap on about an hour ago. I got my parts from a 2000 Tiburon in a junk yard for 150 dollars for everything. You'll need the Spindel Knuckle assembly caliper and rotors. It took me somewhere around 4 hours because it was a pain in some parts. Also your going to want to get your car aligned because mine is way outta wack.
Anyway your car is an x3 good job

as far as lowering and headers I have no clue but all I did as far as a CAI I didnt feel like spending alot of money so I just bought a K&N filter for the car and cut holes in my air box. works good enough for me. Thats my 2 cents enjoy your Accent I love mine