Exaust Questions

Alright guys, I just bought an 06 aveo. fun little car, just wanted to pick some brains regarding the exhaust. 1. If i was looking at getting a little boost in power with a custom exhaust from let's say the cat back or delete the cat all together because my state doesn't require emission tests; what diameter pipe would be best to use and am I going to run into any o2 sensor problems by deleting the cat and resonators?
2. Just for show purposes and adding a little room in the engine bay, would taking off the factory header heat shield and replacing it with header wrap be a bad way to go. Sorry if these questions were answered in previous forums but I'm a new member to this site and haven't found the answers I'm looking for.
3. Finding an aftermarket header for my car in 2016 seems impossible, is there any left in this world or am I "SOL"? Thanks guys