For the scale mate I would do this (cant resist Im a Surveyor..sorry). Your average ceiling (well here in Australia) is approx 2.4...I have scaled this and got 48mm per actual metre. The angle is a bit hard but it will gove you basics. Standard door is 0.85 to 0.9 wide...I have checked this and got 0.85..which is close so my scale is correct. The floor width is 5.16...I would say more like 5.2m as unusual di mensions are rare. The stairway is a standard 1.2 m here...could be different in the States.

Pretty much I have opened it in Paint and NOT altered the image size when scaling. This is a standard thing I do when I do a room etc..I look for doors and assume ceiling height and go from there. You could even scale off the furniture and fireplace as well mate. Hope it has helped in some way.

cheers bullet