Render times weren't that bad just for tests I was ducking under 30secs but for the final it was just about 2min on i7 3960x. if you are just doing render tests then I suggest to change the point density under final gather to 0.1 This will really help with the render times. As for the grass settings there is nothing special just the default settings. I did a quick one just to show you how it works. Dom did a commercial where they used pfx maybe he can elaborate more on this topic.

The type of grass that you are creating should match your back plate. That looks like fall so your grass should match the backplate accordingly.