Just what are you trying to Populate? You've got six spells which will create 3/3 tokens and then the one creature which can create 3/3 tokens. Now
Call of the Conclave may not be a bad rate the five for two 3/3 of
Fated Intervention isn't the best although it is an instant. Producing a token with that
Vitu-Ghazi Guildmage is an absurdly expensive SIX and even using Populate if you already have a 3/3 is still four; it you were getting another 6/6 or even a 5/5 that's one thing but here you're looking at a 3/3. Then you have six spells that add Populate to the effect;
Sundering Growth may still cost the same as
Naturalize but
Druid's Deliverance is a more expensive
Fog (which some will question the value of) and Trostani's Judment is a horribly expensive removal spell at six. I've mention the Guildmage's populate is pretty expensive for what you'll be getting while Trostani is a little better with some life gain upside. Are you going to get enough tokens out to make Emmara worth her cost?
On the Ramp side of things
Honored Hierarch is pretty slow considering you'd need to attack with it and have it live before it starts making mana; pretty much any mana dork is an upgrade here. If
Urban Utopia is in as a cantrip it still may not be good enough because there's no ramp potential here and I don't know that you'll need to color fixing; most anything that will find a land and put it into play is an upgrade here (looking at:
Farseek,
Rampant Growth,
Sakura-Tribe Elder although very off
brand) or something that will let a land tap for additional mana. The
Centaur Nurturer may get you a little life and be on theme but it's way too late for ramp. edit: Looking I see
Abundant Growth is everything
Urban Utopia is at a smaller cost
Conclave Mentor is a cheap bear that will combo nicely with anything that adds +1/+1 counters and can get you a bit of life when it dies; if you had more targeting it might be especially interesting with
Lagonna-Band Trailblazer's heroic ability.
Chronicler of Heroes is another card that would like to see +1/+1 counters letting you draw if you have one when it enter's play.
Centaur Healer is a 3/3 for three that gives you 3 live. Loaming Shamen may be interesting as graveyard hate although it can be a little harder helping you especially when you have other ways of getting thing back without the random effect.
Part of me thinks the way to play Centaurs would be to go with +1/+1 counters.