Everyone has given great advice! I just wanted to add my thoughts too. It was SO hard for me to let my son cry in his rear facing seat when he was a newborn. But, it is so much safter to just drive than to "tend" to them when you're operating a moving vehicle. If the noise is bothering you too badly pull over to soothe him. So many accidents are caused by people turning around to check on their children.
The mirrors can be great BUT they can also be a distraction too. I found that I was looking at my son way too often and was taking my eyes off the road--so just be careful.
And whatever you do. Don't be tempted to turn his carseat around early. It's recommended that the carrier be rear facing for at least the first year. I have known some moms who turn them around early so their child won't cry as much and I don't think that's a good idea.
Safety first!
Good luck and congrats on the baby!
J.
PS.. I just wanted to add that your son will pick up on your emotions. So if he does cry just try to stay calm and relaxed. This will help him relax!