Room size for B&W 802D???

the room size should be OK.
you may want to pull the speakers out as far as you can. First, it will most likely sound less boomy, and second, you will increase soundstage depth. The closer the speakers are to the wall behind them, the less is depth of stage, unless you got some serious room treatment on that wall. But chances are, you may still need some sort of bass traps behind the speakers. What kind of amp? What power?

you'll need to experiment with speaker placement and possibly with bass traps. There may be some suckout on the left side due to the openning into the kitchen/foyer, which will also cause you to play with speaker positioning to achieve proper center fill and soundstage. You'll figure it out as you start setting it all up. Play it by ear.

it will take some effort to find the position for them but you'll get there. Usually the image shifts towards the side with the openning so you may need to tweak the left speaker in your case to center the image. Stereophile test cds work good and you can do it by ear. good luck