Dropping a retractable screen in front of a fireplace is good. That's one of the best reasons to have a retractable screen.
Console gaming on a 100 inch screen is also usually great - much better than on any regular sized screen. Only problem is when you stand in the light path while playing.
As far as projector mounting distance, every projector is a little different, of course, and most projectors have zoom that allows flexibility in distance, but generally, the projector gets mounted slightly behind but close to the viewers' seating distance. Mine is about 16 feet away from a 106" screen. There are projector calculators that will give you more exact distances for specific projectors.