Battlefield Forge and Shivan Reef would make this deck amazing, also wouldn't hurt to add more Seeker of the Way and maybe test Temur Battlerage, give Seeker that +1/+1 and Double Strike for the life gain. Also could try Jeskai Ascendancy.
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Hope you guys enjoy, any suggestions for a side board would be appreciated.
Drop Chief of the Scale, add Butcher of the Horde and you should be good to go.
Also would like to add that I built a deck similar to this a few days prior to seeing your post, mine has zero Messengers and 3 Nissa, with the 3 Collected Company.
Great build, I would drop the Messengers completely, drop the Thoughtseize and add 3 Collected Company, 2 Sword Of The Animist Two Nissa and squeeze in Eyeblight Massacre.