With that size monitor, a 13" will work nicely.
One thing not mentioned is whether his school offers any special deals. Some universities offer 4 year walk-in service agreements with machines purchased through their bookstore or computer store. Covers you the entire time. A colleague's daughter got that when she went to college. I know the University of Virginia offers accident protection (spills, drops, etc.) and provides loaners while being repaired.
I will have to check, I kind of wanted to surprise him with it , the. I realized just how little I knew about macs & figured that I should at least ask him what programs he was going to use. I knew about x code & the adobe suite, I did not know about blender 3-D