I'm pretty new to Yorkie ownership myself, but I will answer the questions I can. I have a 7 1/2 month old, Rowdy. He is absolutely the sweetest, most loving little guy I have ever known. He's 4 lbs, and that seems terribly small to me - I don't think I would want one any smaller. He loves EVERYONE (so far) and I have taken him to a retirment home and I'll tell you, they just loved him and he just loved them. I would think that the standard Yorkie (4-7 lbs) would be necessary to interact with the residents - I think a smaller one might be too fragile - but then I'm a little paranoid about Rowdy getting hurt (he hasn't yet, but I worry). I know the residents were just wild about him, he is small enough for them to pet and easily hold or sit on their bed, so from that perspective, I think a Yorkie would be a good choice. However, as with any new dog, you can get one that is anti-social.
re: housebreaking. Rowdy was not at all difficult. My husband is retired so he was at home, most of the time, and we were just very dilligent at taking him out very often. We did not use treats because he is a very very picky eater and just was not interested in treats. He was 80% housebroken by 4 months and completely by 5 months. I do have a doggie door and he can go out anytime he pleases, so he did not have to learn how to tell us he needed to go out. When we go to my daughters house though, we have to watch him closely because he will go to the door, but does not yip or anything. If we are not watching him - I'm afraid he might have an accident, simply because he doesn't know how to ask to go out.
I have posted this before - I am not a "dog person", but this little Yorkie has completely and totally stolen my heart! I just cannot imagine life without a Yorkie!
Here's a picture of him - now how could anyone resist this face????