sorry for a bit delayed answer, but am I not that active on the forum.
As for your questions. First of all regarding the color, I am using Camera tonemapping and usually agfapan-apx400CD or agfapan-apx100CD cameras.
Smooth shadows come by detailed mesh of the models and geometry of the source of light (not that much though), also out from Env Map.
3D panels are simple, in order to see edges visible as in my hotel exterior renders, I made a little gaps between each panel, like 1-2mm.
All in all, it is mostly up to a detailed and good/precise model as for your questions. But good old rule of CGI quality is 30% detailed model, 30% good textures, 30% render settings and 10% is post production. I always skip last 10% simply because I am not skilled with Photoshop nor I want to spend time on it.
As for my steps, they go as following:
1. Create the model of walls, slabs and roof of main exterior/interior (depending what I am designing) model.
2. Create all openings such as doors, windows as well as fences/railing.
3. Create ground and streets/sidewalks.
4. Make main materials of exterior or interior such as wood/metal material for panels, stucco, concrete, asphalt etc.
5. Put in furniture models and carefully map them when create materials for them.
6. Put in, render preready, plants and trees.
7. Fill in details such as cars, drinks, books etc.
8. Set up rendering settings.
9. Wait till the render is noiseless as possible.
NOTE: it is very important to use layers when creating complex models in SketchUp. Such as "trees", "cars", "details", "furniture" etc.
Check out the print screens below.