The absolute most important thing for him to do is to be able to pass the Corps PT test on the first go-around. If you don't , you end up in remedial PT. Look up the Army PFT, and what is expected of number of sit ups, pushups and running, and it is very similar, if not the same. (Not sure if it is the same as AF because I am not familiar with those requirements).
They do get "yelled at" with cadre "in their faces", but my DS was expecting that so it did not really bother him. However, there were some kids who that bothered a lot, and a few did not even make it through the week! Overall, I think Rook Arrival week was less stressful than he thought it would be. He expected the worst - to be yelled at, to be tired, etc. and I think that helped him mentally.
He will be told when to wake up, when to shower and shave, when to go to bed. At first they have only a few minutes to do things in the bathroom, so have him learn to shower and shave VERY fast! Buy one of those stypic pens, or however it is spelled, the stuff that stops bleeding if you nick yourself.
They don't get weekend privileges until they are "recognized", which is typically sometime in March (you will not see that on a calendar, as it is "secret"). They can leave for most of Parents Weekend - can leave Friday night, but have to be back early Sat morning for formation and some Rook competitions, which are very cool to watch. They have to stay for the football game (this year, just through half time), and then they can leave again until sometime Sun afternoon.
Is your son an AFROTC scholarship winner? If so, he will have to arrive a few days before the general Rook Arrival Day, and there are a few events revolving around that.