Hi! Bant plainswalkers is an interesting idea.
Deploy the Gatewatch is no doubt powerful, and it looks like you have the threshold of plainswalkers to make it viable. Like Brosmanj said, I think the biggest concern will be surviving till that point. I like his
reflector mage idea, and also think
Oath of Nissa will be a huge win for this deck. It will make make sure you hit all your land drops and making casting any plainswalker you draw much easier. Since this deck really turns on at 4 and hits max potential at 6, those land drops are essential. For this reason, it may even be worth considering some mana dorks like Uvenwald Captive.
it may sound crazy, but if you add
Oath of Nissa, you could even consider a one of
Chandra, Flamecaller. She practically wins games by herself, and
Deploy the Gatewatch +
Oath of Nissa gives you plenty of ways to get her in play. Plus it will dilute the plainswalker types you have and make it less likely to hit a plainswalker you already have in play off a Deploy. Just something to think about.
I hope you found this helpful! Good luck and Happy Hunting