adoptees--what should we ask our son's bfather?

We are adopting our 2 year old foster son. His bmom placed him into foster care voluntarily and did provide the social workers with a little bit of personal and family health background. His bdad did not surrender his rights voluntarily, but neither did he try to keep them. He has never met our son, although he could have if he had wanted to. As we approach the day that the adoption will be final, we are trying to put together all the info we can for our son to have when he is old enough to understand and ask questions about his bparents. We are writing a letter to each bparent. From bdad, we would really like any important health info, as well as just general info he might like R to have. The info we do have is of an unflattering legal nature, and we don't want to have just this to share with R. If you are an adoptee, what would you suggest we ask bdad--what might you want to know about your bparent or his family or background? If you are a bparent--what would you suggest? We don't want to offend or hurt this man at all, we just want info for our little boy. Thanks in advance.