i don't think the crop factor of the camera is an issue either, but i don't think you will be doing group shots, at least not easily, and full body will be tight too. your level is not far from your back wall, you will want a minimum of 6 feet to keep your subjects from casting a shadow on the background.
move the level 6 feet from the background and see what you think. my "studio" is about that size, but with lower ceilings and have the same issue with shadows when shooting adults.
PSA: The above post may contain sarcasm, reply at your own risk | Not in gear database: Auto Sears 50mm 2.0 / 3x CL-360, Nikon SB-28, SunPak auto 322 D, Minolta 20