We meet on the second floor of a conference building. So there is a nice big conference room for Sacrament Meeting, and then smaller rooms for classes. On the Sunday we attended, I'd say there were about 100 people at church. Most of the people are American, but the main speaker was Japanese, and I will say, his English was not strong, although his talk was lovely. Foreigners are not allowed to meet with native Chinese citizens for church. The natives attend their own branch of the church (with their Communist Party overseer, I'm sure!) So it's just internationals in our branch, which gives everyone something in common besides our faith: everyone is far from home. That means everyone is super supportive and kind to each other.
I really enjoyed meeting everyone. I went to lunch with some of the ladies during the week, and got lots of tips and advice. I'm excited for the budding friendships I made. They put me on their email list as well, and from the emails I've received, I learned that they have several activities planned during the week. They do exercise groups, lunch groups, scripture study groups, Shanghai walks (where they visit various historic sites or other places of interest around the city), and birthday get togethers.
Hopefully that answers your questions and gives you a better picture of what church looks like in a place where there are no missionaries and no proselyting allowed!