I think you have gotten excellent questions already and I know this is a scary task as I located birthmother and have written her letters to be translated via a searcher. Like you I have not wanted to overwhelm her and jeopardize the relationship and future contact so have only ask a few of the questions above.
I try to envision how I would feel if someone was asking me this question and I was in her shoes. And I also take into consideration that we share a special child. Every letter and word I write I want to be out of love and respect for the birthmother and "our" child.
To help put myself in the birthmother's shoes there was a wonderful letter written by Pedid on another forum ( Tristin's birthmother) and then a letter he wrote about the experience of meeting his birthfamily @ 9 yr's old) Pedid had an excellent way of expressing her fears, questions and concerns and providing information for her son in the future.
You might be able to search the archives and locate the letter?
Adopting from Guatemala, Guatemala Adoption Blog I believe this is the blog that it was on!
Good luck