I wish I focused more on the rocks sooner. Such a energysuck... with 150 energy just to get 25-30 stones a day, this is very tricky if you don't have alicorns, energy crates or gems.
I'll bet they do a five minute unlimited energy deal. Clear your castle, fill the screen with rocks and chop for five minutes straight. I don't think you'd even get enough stones to get to L10 from that!