I have done an event with the orchestra in another room. The sound guy loved it - he basically didn't have to worry about battling the stage sound at all, but that was in a practice room with the walls all treated with acoustic dampening. If they were in just a regular room (say a small hall etc) where he would have had to worry about reflection etc, he would not have been so happy.
Communication was just like with an orchestra in a pit, except we added "Stage Cam" using a plasma on a stand at the back of the practice room for the conductor, and we had "Conductor Cam" on the balcony rail for the guys on stage. Cue lights and coms were run to the conductor.
We used Aviom personal monitor mixers for the orchestra, so they could mix their own private foldback mix based on 8 sub mixes (Male vox, Female Vox, Click, Woodwind, Kickdrum, Percussion, Brass & Strings IIRC)
Venue managed all the catering requirements, so no idea what happened there.
It was corporate awards show, so we only had to do the show twice and the cues were rather basic. It was made a bit more complicated by the fact that the orchestra performed a dinner set - requiring us to quickly create a full orchestra setup on stage for 1 1/2hrs of the show before banishing them back to the rehearsal room for the rest of the show.