This is a really good deck, and it could easily
overwhelm your opponents. It uses a lot of good techniques, and a lot of +1/+1 counters. Some cards that I would add at least to a sideboard would be
Simic Fluxmage,
Lorescale Coatl and
Fathom Mage. Some other things I would add would be some more creatures with evolve, and some instants/sorceries that move around +1/+1 counters.