So are you aiming for this to be a casual deck or legal in competitive formats? The reason I ask is because Earthcraft is banned in legacy, but in casual play, it creates a nice infinite squirrel loop with Squirrel Nest.
For some more general thoughts.
Personally, I'm not as big of a fan of Krosan Beast, Squirrel Wrangler, Acorn Catapult and even to some degree Nut Collector. Consider that both Acorn Harvest and Chatter of the Squirrel have flashback. So when would you have seven cards in your yard to trigger Threshold? Squirrel Wrangler requires you to sack lands - typically not a good idea if you're only getting two 1/1 squirrels. Perhaps he could be useful late game, but I'm not seeing it. Lastly, I can see keeping 1-2x Nut Collector for the repeated squirrel production, but beyond that, they're just awfully expensive for little reward (especially when a single point of damage can wipe the collector out).
You're going to want more ways to pump the fuzzies. This can be done a variety of ways, but I'm personally a fan of Beastmaster Ascension (BA) and Adaptive Automaton. Since you're going to be attacking with the squirrels like nuts anyway (see what I did there ), BA will set off rather quickly and then all the fuzzies are at least 6/6 creatures. Similarly, with the automatons, just name squirrel and they're all getting an anthem effect.
Some other cards to consider: Overrun; Garruk Wildspeaker - untapping two squirrel nests is always fun; Parallel Lives - if one squirrel is good, two is even better; Druid's Call and Lure - pair those two on a squirrel when you have Swarmyard in play and BAM, you're pumping out squirrels equal to the total amount of damage the opponents' creatures can deal.
Lastly, you need to keep in mind that a squirrel deck will have some glaring weaknesses - the largest of which is weakness against flyers. You can combat this pretty easily with either Spidersilk Armor to give all of them reach or Gravity Well to prevent anyone from being able to swing with flying.
I have a squirrel deck myself that my GF loves to play. It can be all sorts of fun, although you have to acknowledge the limitations of the deck (although you cannot beat the flavor). You're welcome to look it over for ideas at http://deckbox.org/sets/133527
One final suggestion, if you go with any of the suggestions I've given above (especially with multiple copies of Parallel Lives), I'd suggest keeping a calculator nearby, as you're going to be generating a LOT of squirrels.
Good luck.