Questions for birth father?

Hello!I'm currently a 17 year old girl. When I was way younger (about 2 or 3), my birth father had to leave my life because, as I was told, he was abusive towards my mother and had a previous criminal record as well. The man I consider my "real" father (the one who raised me to be who I am today) met my mother, then they married and he adopted me. Currently they're now divorced and I have a stepdad as well - I don't think that's necessary info in this case, however I'm just trying to explain everything.Fast forward to today - I just saw that my biological father messaged me on Instagram, and I'm guessing he had found me because I contacted two half-siblings I didn't know about until I was 16 beforehand. He's willing to openly communicate with me, and gave me his phone number for when I'm ready to talk to him. I don't plan to do so until I turn 18 (about two months from now), however, I want to start thinking about what to ask him and how to "act" when I'm communicating with him. What are appropriate questions? Should I ask his side of the story, why he did what he did etc? I'm just feeling a little lost right now and honestly, I'm not sure how to feel knowing that he wants to communicate with me. Should I ask why he wants to talk too?Any advice would be appreciated.