Found bio-dad's email; afraid to click "send"

I'm 28 now, and I was adopted at birth in a private adoption. My birth mom (b-mom) was 19, married to an abuser, and was pregnant by a friend of her husband's. Let's call him George. George is my biological father. My b-mom lied to him and said that the baby was her husband's, and that she was going to have an abortion. She even scheduled a fake appointment and pretended to go to it. Then, she left George and went back to her husband. George has no idea that I exist. After I found out I was adopted (at 18 - yeah, my parents suck sometimes) I found my b-mom's address and contacted her. She sent me the whole story surrounding my conception and adoption, including what information she remembered about George. I met her a couple of years later, and send her occasional updates on my life. I think she wants more of a relationship with me, but I'm not quite ready to go meet the family. I think I will get there eventually, though. I'm really glad I know her, and she's really glad she knows me. I've never been incredibly curious about my b-dad. My b-mom didn't say much about his personality, but didn't paint him as such a nice guy, and I have a really good relationship with my real Dad. The other day I was bored and messing around on ancestry.com, and wondered how much I could dig up on him. 6 hours of hardcore internet searching later, I found him! It's so crazy how much we look alike! We seem to have a lot in common, too. He's a musician just like I am. I also know that he has a daughter of his own, and she's the spitting image of me. I know this because I found her blog - younger people have a much stronger online presence. We have so much in common! She even wants to go into the field I work in now. It's seriously like reading my own blog from when I was that age. Obviously, though, he may not be thrilled with me contacting him, and even if he is happy to hear from me, I seriously doubt he's going to be like "hey, feel free to contact my 15-year-old daughter!" I wouldn't blame him for that in the slightest - what parent wouldn't want to protect their child? I certainly wouldn't ever contact her without his permission. So, I now know I have this sister that seems like someone I'd actually want to be friends/sisters with, and it's likely that I won't ever get to meet her. That is far more upsetting to me than his rejection alone. I have a great Dad, but I have never had a sibling, you know? I'd be such an awesome big sister! I wish I had never found her blog. :( I didn't hesitate to contact my b-mom because I got the impression that she had REALLY not wanted to give me up. It's different with George, though. He doesn't know I exist. What is he gaining from this? On the flip side, though, what is he losing? I get the impression from the stories and music he's written that he's a pretty nice/sensitive person. He's divorced from my half-sister's mother, but recently got remarried. That's about all I know. I'm going to email my b-mom and get her input on the situation, since she knows him better than I do, and has always offered to help me contact him if I want to. I have a good letter written out. I imbedded a few pics of me and briefly explained my life. I make it clear that I'm not asking for a relationship or facebook friendship or money. I'd like a medical background, and I'm open to anything else that he feels comfortable with. I'm not mentioning his kids at all, since I feel like that might make him uncomfortable. I don't even know why I'm writing this post right now. I'm so nervous to send the letter, because I only get one shot at this. I guess if anyone else has any advice, I'd really appreciate it.