Best performance upgrades on my 2005 gto ls2?

I'm looking to make it faster and louder while keeping a good sound. Thinking maybe a cat delete or headers or cai. Don't know which one would be the most effective? If any other suggestions please let me know. Also I've heard that you shouldn't put headers on yourself but how much does it cost to have them put on? And can I put a cat delete on myself or should I have that professionally done too? Thanks