The deck is designed to operate off very few lands, and in fact, you almost never want to draw more than three. Two is plenty. On the other hand, you need at least one forest (or a
Land Grant; for this section, I'm assuming those are the same) to do anything at all.
Number of Forests vs. Chance of at least one in opening hand:
The tradeoff to this is avoiding mana flood. We want to draw mostly gas and not have more than 3 lands in the first 5 turns.
Number of Forests vs. chance of drawing 3 or less in the first 5 turns:
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12 Forests: 81.6%
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13 Forests: 76.6%
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14 Forests: 71.3%
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15 Forests: 65.7%
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16 Forests: 59.9%
(Notably this is not a conditional probability on mulligan decisions, and assuming you only keep hands with 1 or more lands, your chance of flooding is actually a bit higher than these numbers).
Based on these probabilities, I'd say 13-14 Forests + Land Grants is around the sweet spot, also somewhat depending on how many Elvish Spirit Guide or Llanowar Elves effects you choose to include.
To include Wasteland or no? The main reason not to would be (a) poor synergy with Skyshroud Elite, and (b) awkward draws with Land Grant because a Wasteland in the opener may not cast any spells, but also prevent searching for a forest on T1. This leads to unecessary mulligans. I think Land Grant and Wasteland mostly shouldn't go in the same deck.
Treetop Village is a very good utility land but anti-synergy with Winter Orb, and including it turns on enemy Wastelands.
Older Stompy decks that go higher on the mana curve have used Gaea's Cradle but that's not what we're doing here (also, budget reasons!)
