It sounds like you have a good support system behind you.
This book might be helpful, it's free if you have Amazon kindle, inexpensive if not. It might fill in some holes for you.
I actually wrote a book about buying your first horse. Honestly there aren't really any wrong questions to ask, but asking the right questions is really important. You might want to sit down with your trainer and create a list of questions you want to ask.
Also, remember now a lot of people do things by email. So you might be able to avoid some of the phone chatting.
Here is a link to my book. It's free if you have kindle unlimited https://www.amazon.com/Finding-Your-Equine-Soulmate-Buying-ebook/dp/B01N7S6CT6/ref=mp_s_a_1_5?dchild=1&keywords=buying+a+horse&qid=1602962013&sr=8-5