[0] Light leakage - If modeling, you can overlap, flange, or weld joints. Since you're using an existing model, I would load a primitive cube and stretch it like a long piece of moulding, set outside the wall to block the light.

[1] Shadow sharpness - Select the relevant light, refer to the parameters panel, properties tab, and set the shadow blur radius a little bit higher than zero. It will soften the shadow edges, but expect that it will cost some extra render time.

[2] Try render settings with 3 or 4 raytrace bounces and set irradiance caching =>70. If patience permits, engage indirect light, and set indirect light quality =>70.

[3] "P4 texture blur" on the floor - Use an asymmetrical seamless tile image and tile it multiple times in both U and V.

This zip has the image maps and the MT5 for the diamondplate material; increase the value 2 (highlighted) to set the number of times the diamondplate is tiled. The diamondplate MT5 will be in runtime\libraries\materials\0 build materials.

diamondplate MT5

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5