As far as the gaskets, I've heard people swear by cometic. It is a nice concept and design. The MLS gaskets are the way to go, whether it be cometic or GM MLS. My tuner said cometic is the only way to go, so I got the .040 thickness for a hair better compression. GM gaskets are fine for the rest of the gaskets.
http://texas-speed.com/shop/item.asp?itemid=87&catid=36
That is a gasket kit for the heads/cam swap. It also comes with the harmonic balancer bolt. As far as head bolts, GM bolts should be fine. There is a difference between pre-2004 head bolts and 2004+ head bolts, so make sure you select the right ones.
As far as springs, my heads came with comp 921's, which are very reliable, but also come with a huge price tag. The PAC's will be fine. I have two friends that will be running the 1518's in their cars very shortly. Personally, I like the idea of duals just to be safe. PAC makes a 1221 dual spring if you wanted to go that route. Both the 1518's and the 1221's will handle up to .650 lift
For the heads and cam, I would talk to Patrick G or someone else who is very knowledgeable about picking the right combo for what you want.
Hope this helps