OK talk to me, been through this. IOT is very hard and don't expect to hear from him for a little while. My DH did this in 2008 and it is very hard - both mentally and physically.
I live and work in Waiouru so know a few things. OCS isn't the only thing there we are a small camp but we have the training schools - both for Officer Cadets and Recruits but also most of the training schools for the corps.
With his mail, wait to hear from him as to what can be sent, some staff will let them have their mail (and the treats), however some of them make them share everything. I know a few of the staff there, but with posting round last year a heap of people got posted out of OCS and now I don't know who is there now.
If you want to know anymore, PM me and I can try and help you out.