Okay--my sperm donor is my husband
so this is really a different situation than yours. However, since part of what you're asking is about having a biracial child, I can give you my perspective as a parent of one (and the aunt of two others.) I am Caucasian and my husband is from India. My sister's DH is half African American/half Korean. So I think I can draw upon her experience as well as my own and that of other friends of mine when I say that people (strangers) DO and WILL question or comment on children with mixed racial features in public. And not always politely. And it's very unpredictable, so it can kind of catch you off guard. ESPECIALLY if it doesn't just happen all the time, it's more suprising when it does! So that's something to think about.
Overall in terms of looks, I'd say DD is about 60% me, 40% him. She has my hair (med brown) and she's about halfway between us in skin tone--so darker than me, lighter than him. If the three of us are all together, I think it's pretty obvious to most observers that she's our biological child together and that's where she gets her looks from. And even alone with one of us, she looks enough like each of us that we don't get too many comments or questions on her racial background at the grocery store or the hardware place. But even so, I sometimes do get questions or comments. One fast food clerk asked me outright what race her dad was, and I told her that my DH is from India, and she replied, "Oh, I thought maybe her dad might be black, she looks like a half-breed."
Once I had a lengthy interaction in public with an older woman, who was very sweet and nice and was thoroughly charmed by my daughter, and we (me and DD) were chatting and DD was playing with her, and toward the end of the conversation the lady asked me, "How long have you had her?" or "How long has she been with you?" and I didn't quite get what she was asking, and said, "Um, since she was born" and then in a few minutes it sort of hit me that she was assuming that DD was adopted and was asking what age she was when I adopted her!!
My sister is very much more light-skinned than I am and has blue eyes and there is a bit greater difference in skin color/hair type/eye color between her and her DH, than between me and my DH--I'm sort of a bit darker/more olive skin tone and have brown eyes). Both her kids turned out to look significantly more like their dad than like her in terms of skin/eyes/hair/facial features. Since the racial contrast is greater between her and her kids, she's gotten a lot more questions/comments--especially since my niece looked more Asian than anything else when she was born, my sister was CONSTANTLY being asked by strangers when she adopted her little girl from China . . . . Also, in addition to well-meaning comments or questions or staring, they've had to deal with some overt racism and hostility, especially the whole white woman/black man thing that still really gets some people riled up.
Other friends of mine with mixed race kids have also experienced being asked if their kids were adopted, or if they are the nanny, or told their kids look nothing like them. This can be suprisingly hurtful, especially since it can sort of catch you off guard. For us, one of the biggest issues we have with strangers is religious--we aren't Christian and when well-meaning strangers ask DD stuff like if she's excited about Christmas or being good for Santa, it's hard to decide in the moment whether it's best to explain our family religious situation or not.
Family members are not that big of an issue in our case, both my parents and our kids' other grandparents are very loving and supportive and pretty open minded.
As to how any of this applies to you and your situation--the fact that you are a lesbian smc and conceiving with donor sperm adds another twist in there, because if your child looks different racially than you, and you/your child get questions about your child's looks/racial identity (which you WILL) will sort of lead back to the issue of the father's race/looks--which sort of loops into the issue of the fact that there isn't really a "dad" but a "donor." So you will have to decide how open and "out" you want to be about that, in what circumstances, especially because strangers are likely to ask about your child's background more often than if you have a "same-race" child. Do you want to say, "his Dad is white" and leave it at that, or "the biological father is Asian" or "I used an Irish/Italian sperm donor" . . . you know, how you choose to present this info when people are just commenting on your child's looks or asking about them. Are you going to just try to be pleasant and keep the friction low, or take it as a political moment to inform and educate and potentially have an awkward moment there, or what . . . you'll have to consider your feelings about how you want to express your identity as a lesbian single mom to others--And then later on when your child is old enough to be aware of these issues, you will have the feelings/wishes of your child to consider too. Children of mixed races/religions/ethnicities/nationalities/cultures go through some process of having to learn about and integrate the different aspects of their identity and decide how they want to see themselves *and* how they want to present themselves to the world at large. Children who don't know one of more biological parent for one reason or another (like children of closed adoption) sometimes have a lot of questions about their biological parents/origins. And obviously, there are varying degrees of acceptance of gays/lesbians and gay/lesbian parents. So, there are a lot of social/identity issues to potentially contend with there for yourself and your child.
In terms of dealing with comments from family and how they feel about any of these issues (being a lesbian, becoming a lesbian mother, becoming a single mother by choice, using donor sperm, having a biracial child, or D, all of the above) only you can say how they're going to feel about that, and how supportive or unsupportive they will be and how that might affect you/your future child. However, family can be a little easier in some respects, in that once they know, they know, and that might be the end of it. And if you know they are going to have a problem with it you can just choose to avoid them! Whereas with strangers it's an issue that is going to be unpredictable and ongoing. So that's something that you need to be prepared to potentially deal with if you are going to become a mother of a biracial child unless they just come out looking like you anyway!
Now, obviously like I said my situation differs in that I am married to a man who is the father of my kid. I picked him to marry and have kids with because I love him and thought he'd be a good husband/dad, and he's around in the picture as the father. I like his looks, I like his culture, I love my husband and our family, enjoy our differences as well as our similarities, I think my daughter is beautiful inside and out and wouldn't have her any other way, and we both are trying hard to give her a positive sense of her identity as a person of mixed-racial/religious/ethnic/cultural/national identity. I have no problem inherently with the idea of mixed racial origins. Thus said, there are some extra challenges to being multicultural and being "different", both for children and their parents. I will put on my flame-retardant suit here and say that if I were single and considering becoming a mother through donor insemination from a sperm bank (which I did plan to do myself at one point in my life, even had all the tests done and paperwork filled out) I would probably try to look for a donor of the same racial background and somewhat similar looks as myself, just to maximize the chance that my kid will look a bit more like me, and also to keep life a little bit simpler for myself and my child and reduce the variables.
: I mean, in this process, you are already cherry-picking a donor of a catalog on the basis of a brief description and some genetic information and some vague descriptions of their looks and history and personality--you're not selecting them as a person, but choosing them for the effect their genetic material will/might have on your potential future child's health, physical appearance, and other characteristics which may or may not even translate very directly to the offspring (sense of humor, speaking a foreign language, having graduated college, musical ability, etc.) If you were committed to intentionally conceived a biracial child, I wouldn't try to dissuade you--but hey, you are aware that it's a less common circumstance in your circle of friends etc., and you have some questions about how you might feel about these issues while raising the child, and you asked for input, so I'm giving you my honest opinion even though our life situations are not exactly the same. Would you consider being less particular about some of the other desired qualities of the donor in order to give you a bigger pool of potential donors? Like, f you lowered your height requirement somewhat, might that give you a slightly larger pool of African American donors?
ETA: not sure where you have cross posted, but you might check out the multicultural families forum, either post there or just lurk and check out other mom's experiences with raising biracial children.