As far as your mana, I think you have it about right. I would probably make it 14 islands and 6 swamps instead.
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Rather than playing the gomazoa, I would play recoils. Also, I would get my hands on some counterspells. Take a look at my deck and see if you get any ideas. http://www.mtgvault.com/ViewDeck.aspx?DeckID=142186
I think this is a pretty good base for the deck. From my experience, Keening stone is too slow without some mana acceleration. Maybe you could consider going blue green with this deck. It will also feed into the hedron crabs. Also, disperse can help with a wider variety of your opponent's cards instead of unsummon. Check out my mill deck. http://www.mtgvault.com/ViewDeck.aspx?DeckID=142186