Welcome to coal. Your 503 will work well for you--central fireplace and central staircase with ceiling fans. Should be fine. Nut is my coal of choice.
I have been heating my house, which is about 3000 sq ft, entirely by a 503 and it works well. Saving alot of money over oil.
One arcane issue with the 503 is excerpted from a previous 2011 post of mine: "One other thought regarding operation of this particular stove concerns the bricks just inside the firebox door. There is some wiggle room with these bricks. I noticed that the bricks have a tendency to lean toward the fire, i.e. away from the door and into the heart of the stove. If that happens, pieces of coal can get behind the bricks and eventually the bricks will break and need to be replaced. Simple fix that has worked for me is to wedge a piece of rebar--cut so that it runs the width of all the bricks just inside the firebox door--so that the bricks are held back tight against the front of the stove (back toward you the operator and away from the fire). No more wiggle room!" This has worked over several seasons.
Regarding cleaning of the 503 with a SS liner installed--easy to do from below. Use the most flexible rods you can buy attached to your chimney cleaning brush. Run the rods up through the ash pan door. Wear gloves as bloody knuckles take the joy out of the job. At end of season, volume of coal dust from clearning is about 1 gallon.
Enjoy your stove!