Skipping over the bulk of the conversation (short on time)...but a few ideas come up:
Your dd and my dd are the same age. One thing that has really helped make her birthparents more real, and less strangers, is a lifestory book. Polliwog, I can't remember...do you have one? Could you make a very simple one on shutterfly or booksmart? In there I spend several pages talking about her parents, about their families and background, and about the decision not to parent and the choice of adoption. It's all very simple, obviously...when I wrote it and started reading it to her, she was two...so it's on that level. (And also, the info we have is very limited.)
I agree that a four year old is going to have a hard time truly *getting* the idea of birthparents, but dd has heard this story so many times that she knows she has two moms and dads, and knows that two of them live in Korea. She asks about whether they miss her, and where they work, and if she can give them drawings and presents. We only have a picture of her mom, not her dad, but she's latched on to that picture and likes looking at her face, and talking about what they have in common. She asks questions about her dad, too.
Now...if we took dd to Seoul this year and she met her parents? I'd imagine they'd be filled with emotion, and might want to swoop in and do some serious hugging. I can't know until I'm in that situation, but I think I'd be okay with that. Don't get me wrong...I'd be mentally on guard for how dd is doing...but if that's what they need, and where their emotions lead them, then as long as I have reason to believe they're common-sense people who will have dd's needs at heart, I think I'd be willing to understand an emotional overflow--even if dd was a little scared by it.
Part of the reason I'd trust the process is because I trust her to "get" it. I feel like it would take her a while to put the realness of her parents in perspective, but there's already a framework in her brain where their realness can go. Perhaps it would be worthwhile to work on that framework more with your daughter? As for sex ed...Dd has been asking about the birds and bees since she was three, Ds even earlier (as they got siblings), and by four they both knew about sperm and eggs. It's not really a charged subject for a little kid....and besides ;), they really like knowing it's how almost EVERYTHING is made...flowers, puppies, the frogs in the pond. It makes more sense when they know about eggs and sperm. ;)
It's just my opinion, but I wouldn't worry about him being too touchy-feely at this first visit. I'd let your daughter get to know him as he is. Maybe he's an emotional guy, and maybe she'll recognize that in herself some day. You can even make that part of her framework for him, if his tendency toward hugs and emotion continues. You can help her put it in context. I'd imagine dd would understand something like "Here's a picture of your dad. Remember him? He gave you all those hugs when you met him last time. I bet he's really missed you and was very excited to see you after so long." You could talk longer about whether she liked those hugs, if she minds them, or if she'd rather you asked him to change things on her behalf. As she gets to know him more, I'm sure she'll get used to what he is and who he is. I'd worry that asking him to behave a certain way, or be a certain role, would be damaging at the start of a relationship that your daughter and her dad are going to have to forge (to some extent) on their own for the rest of their lives.
As for dd's lifebook, this is what we have written:
DD, do you know that all babies begin the same way?
It's true. It takes two people, a man and a woman, to make a baby. [There's a picture of an illustrated Asian man and woman..the woman is pregnant and you can see the image of a baby in her belly.] Everyone in the world has a birthmother and a birthfather. You do, too. Your birthmother and birthfather are Korean. We call the woman who gave birth to you your Omma, and the man who helped make you we call your Appa. They are your birthparents.
You were conceived by your Omma and Appa, your birthparents, near the beginning of December in 2006.
See your belly button [there's a picture of dd pointing to her belly button]? That belly button is a reminder of when you were very, very tiny and in your Omma's belly, growing and getting ready to be born. For nine long months you stayed cozy and warm inside your Omma. Everything your tiny baby body needed to grow was given to you by your Omma's body through your belly button. You stayed in her belly until you were big enough to be born.
Then, in the afternoon of [month and day], something very special happened! You were born! [Illustration of a newborn baby...we don't have any newborn pictures of dd]
Your Omma gave birth to you and you took your first breaths of air. You weighed 7 pounds, 6 ounces, and you were 20 inches long...a very healthy baby. We don't have a picture of you then, but you had dark eyes and a little round face, and very short fuzzy hair. This is [name of hospital], where you were born. [Photo of the clinic where she was born]
Then there's a page on the zodiac, and the year of the pig
Then there's a page on the name her parents chose for her, and what it means
Then there's a page about the city where she was born
Then back to her parents....
Your Omma and Appa lived in [city]. Your Appa's name is [name name name] and your Omma's name is [name name name].
Your Omma has two older sisters and an younger brother and sister. She was born in [name of city and state] in the south of Korea, which is famous for its apples and for very lovely women. Her parents, your grandparents, are farmers in [city]. Your Omma worked in [city]. She described herself as being reserved and quiet. She was [age] or so when you were born.
Your Appa is an only child. His father works as a security guard at a temple. Your Omma says he was friendly, even-tempered, and quiet, and he worked in [city], too. He was [age] or so when you were born.
Your Omma and Appa lived together for many years. They had some grownup problems and they knew they wouldn't be able to to take care of you when you were born. Sometimes people aren't able to take care of a child, any child. It's not your fault they couldn't take care of you, DD.
This is a picture of your Omma when she was six months pregnant with you! [photo of her mom] We see so much of your Omma in you. Sometimes you smile like her. You also have her eyes, and the shape of her face, and we think you might have the same hair that likes to fall forward. Your Omma looks friendly, like you do.
Then there's a page about her mom making the choice to live at a maternity home with photos of the people her mom knew there and photos of where she lived. Text: When your Omma knew she was pregnant with you, she knew she wanted to take very good care of you and make sure you would have a good, loving family. She decided to live at a place called [name], with a very nice woman named Mrs. [name].
Mrs. [name] said your Omma is a kind woman. She described your Omma as "calm and bright." She said she wasn't very talkative, but was comfortable to be around. Your Omma lived at [place] for the months before and after your birth, and the women there took very good care of her. Mrs. [name] said that your Omma loved you very much, and wanted you to grow up with a family. Your Omma made the decision for you to be adopted. We're sure it wasn't easy for her to make that choice, but she believed it was the best decision.
Then the book goes on into dd's life...where she went after she was born, her first photos, the foster families she lived with, why she was moved, and what was going on behind-the-scenes with us so that we could adopt her. We feature her foster families quite a bit, her foster siblings, the first photos we ever saw of her, the first time she got a package from us, her first Spring in Korea, the first time we met her, how she reacted when she had to leave her foster families, and how she reacted as she got to know us. After all that, there's a page with pictures of her four families...her birthmom (again...wish we had one of her dad!), her first mom with her, her second foster mom with her, and a photo of her with us that first day in Seoul. Underneath it says:
All the people who love you...and now you would have a new family. A family forever.
DD, do you know that families are made in different ways? Some children join families by birth, and some join families by adoption. When you are adopted, that is forever. You will always be our daughter, an we will always be your Mommy and Daddy. When you join a family by adoption, you have two sets of parents. Your birthparents that we call Omma and Appa, and us, your Mommy and Daddy. You also have many people who have loved you and taken care of you. So many people love you, DD!
Then it goes on to describe our first few days and weeks as a family...it introduces my extended family and dh's, and shows pictures of what she liked to do when she first joined us. There are pictures of her baby annoucement, and of us with the judge on the day she was adopted. The last page says:
DD, your first name means shining light. It's a form of your great-grandmother [name]'s name, and we think the meaning is beautiful. We also wanted you to keep the name your Omma gave you, [name], because that is your Korean name and it is an important part of who you are. [Name] and [Name] are your two family names.
Both names were given to you with love. Both families are a part of who you are and who you will become. Our little light, our little river and grace, our beautiful girl. We love you.
I hope you don't mind me sharing that, Polliwog. I know you're a very experienced adoptive parent, but I wanted to share some idea of what dd (at four ) knows very well about her parents and conception/adoption. Obviously we've toned down the details in her parents' relationship and in the difficulty of choosing adoption...we'll fill that in as she asks...but I did want to give her as much basic information as I could about her parents and their personalities. I so wish we had more information, or a photo, of her father--I think it would make it easier for him to be even more real for dd.
Maybe it's all just wishful thinking, but I'm hoping that if we make her Korean families (birth and foster) more real to her, then when she meets them she'll feel like they've been a part of her story forever. She'll know a little of what to expect from them, and know (through the book and our conversations) why they would have an emotional reaction after not seeing her for so long. That's not to say that their reactions might not weird her out a little (or a lot) at first, but that when we talk about those reactions I'll be able to put them in context, and she'll understand better what's happening and why.
Hope that helps. Best of luck to you...I'm sure it's not easy.