Congrats on the decision and welcome to Terp Nation! Your son made a great choice!
FWIW, I would at least wait until orientation so you have the opportunity to inquire about the current recommended minimum specs for CS.
Four years ago, we bought our son a Mac through the university as they have a special arrangement that if you buy through them and something should happen that you need to get your computer repaired, they supply you with a loaner. It’s a pretty nice insurance policy. Dell is the other option to purchase for that arrangement.
http://it.umd.edu/act/index.html
http://it.umd.edu/techsavings
http://it.umd.edu/techstore/index.html
My son also recently bought himself a Surface Pro which he takes to class with him for taking notes. (Don’t ask me details of whether it’s a 3 or 4 or where he bought it as I have no clue - as I said, he bought himself - internship $ comes in handy!). He says the Surface Pro was a great purchase and he really enjoys using it.