I run Autolite 104's with my setup (check my sig) and they work great. I actually put in 103's and the car wouldnt idle for ****, so I stayed with the 104's. Also, stay away from Iridium plugs, and get the copper 104s, they are cooler, and cheaper too....
As far as the Plog, Just soak the exhaust manifold bolts with WD-40, or penetrating fluid. It will make it a lot easier to break them loose. It's easier if you remove the top motor mounts, and move the engine forward/backward in the engine bay, so you have more room to work. When I put my headers on I just used the stock exhaust gaskets that were on there, and they sealed fine.
As far as the throttle body spacer, it will reduce throttle-body temps, but wont decrease the air temperature at all once it's in the supercharger, so it's only used to keep the TB/sensors cooler, or for a Meth/Alky injection setup.
For the tune, you should be good to go with your overkill PCM (what I have, love it) But you really should get a scan tool, to see if you're getting any KR at all before the pulley drop, and especially after the pulley drop.
