Hi there Ernie..
Airbox wise you won't find any mods to purchase except a K&N filter. You can remove some babbles, known as gutting the airbox. That would help flow. We can definately guide you through that.
As for the exhaust. The biggest restriction is the front exhaust manifold. A ported manifold has been found at W-body store around $80, looks stock and works good to our experience. A high flow cat can help down the road, however at this point your car doesn't flow enough that you will benefit from it.
As for ZZP and service, I wish you luck and suggest forming your own opinion. I would suggest contacting www.intense-racing.com
also. They probably have more NA mods available than ZZP.
You are going to notice a little increase in power, however should not expect a decent HP number from it. Our cars are designed rather well, until you get serious about modding or have a supercharged engine.
As Gogo mentioned, you should be aware of a possible motor killing weakpoint of your motor, the upper intake manifold.
Here is a link to something all naturally aspirated 3800 owners should know