The size of exhaust clamp you need will most likely be specific to the exhaust that you get. Most come with band clamps when they are necessary. For header bolts, I like these ARP Stainless bolts

http://zzperformance.com/3800/bolts/...der-bolts.html

They're a little pricey, but if you're getting stainless headers, they'll make them look a lot better.

The dipstick should be the only issue with header install.

Block the EGR if you're going to be tuned (Check your local laws first, you might need it to pass emissions if you have those). It deposits a lot of carbon buildup in the engine.