Get gears first. I have 3.73's, but kinda wish I went with 4.10's in my AOD. Still the gears made a big difference in acceleration and is by far one of the best mods you can do!
Then do your exhaust. I would stay away from equal length headers, I guess I'm just not a fan. Their a pain to install, and you loose some low end compared to unequals on a fairly stock stang. The equals scavenge more then unequals. The more a header scavenges the less tourqe it will make. Hp will probably be close to the same. If you want more tourqe and hp out of a header get longtubes. I have the same BBK chrome headers you want. They are a pretty decent header, But be prepared for them to turn blue. I have never heard MAC flowpaths so I can't really make a decision on them. I do like the sound Dynomax or Magnaflow mufflers though.
Pulleys are a great cheap bang for the buck. I personally have never had a problem with my alternator charging while running the pulleys. My autometer volt gauge reads 13 volts at idle and 14 volts while driving, so I don't see what all the whining is about
Hope this helps to clear a few things up for ya.
-Craig