Well.......before I finished your post, I initially thought, "How could you tell the story of someone's adoption, w/ focusing on the parents?'.....but I understand what you mean---I think?
Because you had a longer than average time with the birthmother; and because you have a very open arrangement.......I'd simply start talking about the birthparents and what happened that you 'came along to match with her'. Yes, it's too early for the details now....but I'm a firm believer in talking about adoption as an everyday thing. By doing this, it becomes something 'natural and comfortable'.
Every single person I have read about, or have seen interviewed, that felt 'empty and/or less than', due to their adoption.....came from a home where adoption was not talked about openly or 'normally'. The child was either not told they were adopted'....or 'treated as second best because we really wanted a bio child'.
Just keep talking
Sincerely,
Linny