Remember: although optimizing textures size, lights and "general rendering setting" speeds the work, overdoing it, can ruin the end result.
Well known tool in the community of 3D artists named 3D Coat, recently upgraded to version 4.1.
Always it is extremely difficult to tune adjustment of 3d modeled on real image. I solved it by learning how to deal with a real camera and used it in the virtual world.
Every project I start with collecting information: drawings, textures, photos etc. Professional architecture photos help to understand the atmosphere - to play with light and shadow and to create realistic details of the environment.
If you're trying to create something realistic you need to make little details which you didn't even noticed before, you may think that they are not needed or no one will notice, but the trouble is that exactly these details have the most powerful impact in overall.
I think I have been never satisfied with my results because I know it can be better and I don’t have much time to work on them to reaching almost perfection. However, every project has a time limit hence we gave up upon it