Give that a read first.
Before you get a K&N check out the intake options. A good safe pulley size would be a 3.5. You should get minimal knock retard with that and some basic mods(intake, spark plugs...). As far as upgrading your brakes there is a reason they came with drums from the factory: rear disc was not needed. The only reason I can think to switch to rear disc is so you can spend more money on rotors and pads.
For a chip you need a reflashed PCM, there are a few vendors you can go with, shop around, ask for opinions(theres a lot!) and go with what you feel comfortable with. Same with headers, there are a few companies that offer them. However the headers were not designed for an H-body and a few things will need to done to get them to fit.