Nckbella,
Yes, u can choose a roommate. But that's only when they give u permanent accomodation.
During temporary accomodation if u have severe problems with other roomies in your flat, they might move u somewhere else.
Each and every flat has basic facilities, but not all the buildings have gym. If they have gym, most of the time they're in quite bad condition, so 90% of the crew go to real fitness clubs and pay.
There r not enough crew buildings, so most probably u will be put in hotel for a certain period of time. Some hotels r nice, some r bad.
My advice to u is: think very carefully before joining this airline. This company has many inner problems, and doesn't treat crew very nice unlike EK.