Well, as far as free models go, Walli gave planet side some good models, the pine trees in "At Peace" are those. The grass is actually the stuff Walli has on NWDA, and is of the highest quality, I recommend getting it, it's not expensive in the least. The windmill and cottage were free on Ashundar.
As for render times, depends. All the tweaks needed to have high density populations looking good (soft shadows, higher AA, Quality settings) add alot to render times, but not as much as say a boat load of water and reflective shaders everywhere. If I recall, At Peace completed in under a day of rendering.