Issue when rendering a scene in Cycles. Everything dark (with light) and objects move

I’m trying to create a beach scene with a hut and some grass but for some reason (when trying to make my grass denser) the whole scene now screws up (hut moves up and no lights render) when I try to do a final render. When I do a preview render it looks good. Here is the complete project if someone can help me figure this out: Thanks in advance!

What are your PC specs? Scene as it is right now takes around 7 Gb, breaks 2 Gb nvidia (no GPU rendering) and slowly does run on CPU. Is there any reason to use Experimental Cycles feature set?
I would suggest scale up camera object (this wont impact rendering) so that it covers scene and model plane to be barely outside camera Object. You will need much less particles then.