First off, welcome!
Yup, that is normal poop.
Get him a water dish he can hide under. Wal-mart has some for around a buck right now.
Adult snakes eat adult mice, usually, no matter how big the snake gets. On rats, he might gain too much weight... but he might not.
Plus, corns really love rats.
You will hear from people who feed rats exclusively, and people who feed mice exclusively.
Make sure the very hottest it gets anywhere in the tank is 85 degrees. Believe me, you will be heartbroken when your snake burrows and burns himself. Burns are ugly and painful and expensive to treat. A corn will not move when he starts to burn.
Corns don't need to be that warm, generally. It doesn't matter if he never burrows. My corns are usually on their cool sides and are cool to the touch.
In fact, since it is summer, your corn doesn't really NEED a heat pad, except maybe to digest.
It is much safer for it to be too cool than it to be too warm.
Congrats on your gorgeous baby.
Oh... signs of neurological damage would be if you can flip him on his back and he doesn't self-correct quickly, or you see him moving like a drunken snake.