How exciting for you. But yes, keep a level head.
Ask about vices (cribbing, weaving, food aggression, etc.), any old injuries you might need to know about, how he gets along with other horses, does he need to be shod, what supplements, if any, he's on, does he load well, stand for the farrier, bathe, does he accept paste wormer, etc.
All the things a well trained horse should already know how to do, basically.