Well I can tell you some value ranges that I use in Indigo I’m sure they’re not that different in Lux. Phong materials using the high exponent range will enable you to recreate a lot of varying materials. For brick/ concrete/ stone I use a phong material with low IOR, 1.1 or slightly higher with a low exponent also, say 45-55.
Wood, also phong, IOR 1.34 -1.36 depending on the finish of the wood exponent between 250 - 400 higher values more varnished wood. Grass, similar IOR very low exponent 6 - 8. Remember those are Indigo renderer values.
For realism, every material you use should at least have a colour map, bump map and specularity map
Try any particle grass tutorial, only do a much small patch. under modifier tab convert to mesh object. This will create a lot of grass blade edges, to make actual blades of grass go to edit mode, select all and in top view looking down extrude out to get the correct thickness. Duplicate this little patch of grass using Alt - d as opposed to Shift- d and fill out the areas where you want it. The other alternative is to use a tileable photographic grass texture (with bump and spec maps).
The last render is quite a bit better, lighting is very good.
The environment map you are using is all sky, with the reflections in the window and background it kinda makes it look like the house is floating like in pixar’s Up. An env map with a strip of land might be an improvement. The drive way brick texture is also still a little bit to large.
Hope some of that helps, I think you’ll get a good result by tomorrow.