nice work. Really original!
Regarding grass looking flat and billboards/planes for grass vs indivual strands:
From what IVknow you can get individual strands for < 100kB UE4 resource size, which is mass painting ready.
Over in the pricing discussion I posted a pic with such an asset. The grass is no single plane but individual strands (each one with alpha), which shows in the shadows and keeps it from looking single-plane-flat.