Simple answers, in sequence:
1. No, its very nice especially if you know him/her.
2. Address your ALO by their rank and last name unless they've given you something different to call them.
3. If you're not an applicant/candidate then you're technically not their candidate. However...any student can contact any ALO, but especially the one assigned to their school, at any time. We're here to help, whenever we can!!
Steve
USAFA ALO
USAFA '83
(received a Christmas greeting from a candidate on vacation in Tahiti today!)