i won't be using facebook to stalk him or anything like that. i just wanna get a general feeling for him. so that way i could be prepared to talk to him about any mutual interests that we might have. it was really awkward meeting him the last time and i think knowing a bit more about him would make it a lot more comfortable.
That was my feeling too when I made the suggestion to you. I think knowing something about him will help you to feel more comfortable and, perhaps, find some mutual interests to help you feel a little more connected to each other.
And, if your mom has his e-mail address, I think you should write to him, just to "introduce" yourself, and tell him about yourself, so he'll start to get to know you as well, and that will help him to feel more comfortable when he visits, because you won't be a total stranger to him.
I don't agree with the people here who are telling you that you are selfish or thinking only of yourself. This young man is your half-brother, and you want to have a relationship with him, hopefully a good relationship, and there is nothing at all wrong with that.
Obviously, your mother's relationship with him, and their feelings about each other, are likely complex, and colored by past events and a lengthy separation, and their relationship is really quite apart from the sort of relationship you are seeking to have with your brother. They might need to spend considerable time together, without including you, in order to work on their relationship, and I think you can understand that. For them, this visit is a re-union, for you, it's the opportunity to get to know someone who has the same mom you do, but whose life with that mom, and without her, has been quite different than yours. And, for you, it's also a chance to now have a big brother in your life, and to understandably want to get to know him better.
Your brother and your mom have a past relationship, but you and your brother are starting from scratch--you'll hopefully be forging a new relationship with each other, and there is no reason you shouldn't be able to think about that, and focus on that aspect of the situation--it isn't being selfish on your part--you are adjusting to the whole idea of even having a brother in your life, and that seems very normal to me. It's great you have such a positive attitude about wanting to have a relationship with him.
My mother, when she was about 11 or 12, very suddenly found out she had an older half-brother she didn't know about when he showed up, totally expectedly, on my grandparent's doorstep looking for his father. My mom did not even know her father had been married before, let alone the fact that he had children from that first marriage. So, that situation was more than a little awkward, and confusing, and jolting, for her, and her father also had issues he had to work out with his son that had nothing to do with my mom. But my mom welcomed this new brother into her life, and they formed a close brother/sister relationship that lasted for the rest of his life. He very definitely became a part of the family.
Getting to know someone is always a little awkward at first, and you don't know yet how your brother feels about getting to know you as a new sibling in his life, so put your expectations aside, and just take it as it comes when he does visit. But I do think that if the two of you can connect by e-mail, before the visit, he can get to know you as a separate person, apart from your mom, and you can get to know him, and that might help to make your face to face meeting a little easier for both of you because you won't be complete strangers.