Your son will compete for graduate nursing education through a program called Long Term Health Education and Training (LTHET) or USHUS. He will not be eligible until he has 5-13 years AD at the time the school start date (LTHET). OERs, GRE score, PT scores, senior rater recommendation, AOC consultant recommendation, number of deployments, and GPA all play a factor in how competitive someone is for selection. Number of slots per program also vary per fiscal year.
Info about these programs aren't something that's pushed to cadets in college, nor 2LTs.
Keep in mind, the first few years he will be learning his job. The hospital won't have many (if any) slot allocations for "nice to have schools." If your son plans to attend all the training/assignments you mentioned, he needs to earn the EFMB first (or CMB...not a CAB).
When I was selected for LTHET in 2008, I had two platoons with the 506th IN REG (Band of Brothers), I was the MEDEVAC officer for Sadr City, a Masters in Information Technology, I was a CIO for Winn Army Community Hospital, and 4 (or 5...I can't remember) top block senior rater OERs.
He will have maybe 2-3 OERs as a floor nurse on a ward before he wants to apply...
I'm saying all this to say,
Med-Surg for 3-4 years before he can throw his hat in the ring, even then...it's closer to 6-7 before the AMEDD will take him seriously.
