1) Yes, and no. It's harder than it looks in pictures, but's it's simple to the point where you won't destroy anything.
2) Technically yes, but just keep the stock one around if you need to get some work done on it.
3) You will get in the neighborhood of 0-10HP depending on a ton of other factors that I won't discuss. Yes, it does actually give better sounding exhaust and engine, and better gas mileage!
If you need help, let me know and I can take pictures of where things need to connect to etc. Look at the image on my cardomain page, it shows my CAI installed compared to stock.