You choose what children you take, it's all up to you
Depending on your state's regulations, room sharing should be fine.....here in AZ, you can have multiple kids in a room, but if one of them is over 6yo you can only have the same gender share a room, younger than 6 can share with opposite gender (this varies from state to state, though).
We've been fostering for almost two years, and have had wonderful and frustrating experiences.