First off, thank you for actually following through with the directions stickied at the top of the forum. I was starting to wonder if anyone even read them. So to that end, you have my undivided attention as I'm happy to help whenever possible.
So, with no further ado, the deck.
As I see it, you're not too far off from being a mildly competitive deck. A friend of mine piloted a Selesnya aggro build to a top 300 finish at GP Vancouver this weekend and, in actuality, would've made day 2 had he not been robbed by a total BS judge ruling.
Having said that, you are a bit over-crowded at the four-drop and have some sub-optimal choices in your deck at the moment. I'll go through this card-by-card to help out as best possible.
Elvish Mystic - typically a good dude, but normally reserved for most mid-range decks which, I would argue, you definitely do not want to be. Mid-range decks have access to a LOT better tools than you and will just ruin you if given the chance, so let's not venture down that road. Additionally, while the potential second green is nice, it just throws you off as it doesn't really help you meet WW casting costs like on Precinct Captain. So I'd start by dropping these (don't worry, I'll give suggestions for what to add back in shortly).
Precinct Captain - also typically a solid dude, but again I'm not sure he's what you're looking for at the two-drop. I wouldn't drop him just yet, but he's going to be tough to cast consistently with a WW cost (without messing up the rest of your curve). But, if you do intend to keep him in, I would go up to 4x.
Wayfaring Temple - man he sounds good doesn't he? Just one problem, without a bunch of reinforcements, he's just a 1/1. I honestly don't know that you're going to get his populate trigger to go off without trample given that many opponents will see the value in that and will stop him. To that end, I'd probably have to say to drop him... sorry... but he's worth $0.30 for a reason...
Trostani, Selesnya's Voice - as far as pieces go, this is a good one, especially considering what you're up to. I would keep her in as a 2x and just leave life alone there.
Armada Wurm - the idea of getting 10 trampling power for 6 is pretty solid, no? I like him more than he gets love these days and would suggest running 2x of him in the deck (but cut the other one as you don't want to flood the top end of your curve). He'll be a crazy life swing if Trostani is out and can provide an endless stream of wurms... good times.
You're solid on the Charm, Advent, and Call of the Conclave at 4x each. I would suggest moving Rootborn Defenses to the sideboard as it's often just a dead card forcing you to keep three mana open. Then again, if your local meta has a lot of removal floating around or just a bunch of control decks, feel free to run 2x main.
Unflinching Courage - this card is good not for the trample you cite, but for the lifelink it provides. You can move these to the SB to use against aggro decks that are trying to race you.
Growing Ranks - tempting isn't it? Just one problem, this card costs four to cast and doesn't affect the board in any meaningful way AND requires you to have a token in play for it to even do anything for you. Compare it to Assemble the Legion (admittedly a very different card that costs one more) where the five cost might not affect the board immediately, but it produces the tokens all on its own, no other requirements needed - further, it accelerates to the point that it ensures you will eventually win if the board is just flooded. To that end, I would drop these too.
Heliod, God of the Sun - as much as I'd like Heliod to be good here, once you've dropped all those other pieces and move more toward an aggro shell, he won't be nearly as useful. Further, he's unlikely to ever become a creature AND paying four for a 2/1 isn't my idea of good value. I'd drop him too.
Grove of the Guardian - this too is tempting, but it's a trap. The likelihood you get the 8/8 isn't very high nor are its chances of staying in play. You would be better suited running 2x Selesnya Guildgate until you can compile a playset of Temple of Plenty when Born of the Gods hits.
For the SB, I would keep the 2x Sundering Growth and drop the others... as there really won't be instances where they're as relevant as you think.
So, in sum, that's:
-4 Mystic
-4 Wayfaring
-1 Armada
-2 Rootborn (to the SB)
-3 Unflinching (to the SB)
-2 Ranks
-2 Heliod
-2 Grove
That's 20 cards down... ouch... but don't worry, there are some really solid options out there to slide in... and if you act quickly you can get them before they go back up card of Born of the Gods making W/G more accessible.
+4 Soldier of the Pantheon - for one you get a 2/1 (already off to an aggressive start) who has pro-multicolor (take that Burning-Tree Emissary) AND gains you life... what's not to love (note this is probably the most expensive addition to the deck).
+4 Experiment One - he might seem like a silly little 1/1, but if you consider that he grows every turn and can regen himself only to grow again in response to a Verdict or most other board wipes, well... what's not to love?
+4 Fleecemane Lion - better hurry here as these kitties were at like $9 earlier in the season and could jump back up soon. This is another 3/3 for your stable to go with all those centaurs, but who can also become quite the little nightmare if made monstrous.
+3 Spear of Heliod - one of Selesnya's advantages is that their stuff is, on average, bigger than their opponent's... why not further extend this situation?
+3 Banisher Priest - he's a bit behind the curve you're typically aiming for, but on the flip side, he's removal and tempo advantage (AND he can remove any creature, including the gods when they're online). Just be wary as he is a bit of a target and can easily lead to you getting two-for-one'd if you attack blindly without keeping their kill spells in mind.
+2 Ajani, Caller of the Pride - okay, maybe these will be the biggest investment, BUT, they have quite the return on them as a 5/5 wurm token does wonders when given flying a double-strike. Just mull that over for a bit.
So that should bring you back up to 60. You'll be a LOT more aggressive but also a lot more consistent.
A brief aside on Voice of Resurgence, I've been on the receiving end of some serious Voice beatdowns, but I still am not convinced that they're a MUST for this deck. Obviously they have some serious power (notice the $40 per price tag), but given the pieces you're sitting on, you should be solid anyway. Further, as RTR will be rotating out in the fall, it would REALLY suck to drop the cash now unless you're running this week-in-and-week-out.
For the SB, after the changes I've suggested you would be sitting with the following:
2x Sundering Growth
2x Rootborn Defenses
3x Unflinching Courage
You should add the following:
2x Mistcutter Hydra - might as well hate on blue decks while we can
2x Skylasher - same story, different dude
2x Last Breath - seems silly, but you NEED a way to deal with Master of Waves (how convenient)
2x Glare of Heresy - deals with opposing threats pretty well, ranging from Detention Sphere to Elspeth (kind of a deal breaker against you).
That would give you a full 15.
Anyway, I hope this helps. Obviously I know you can't just order up the entire list of changes, but work toward it with trades and such and you should be pretty set moving forward. Let me know if you have any questions, otherwise, good luck!
I know it's a pricey game to get into, but realistically, this list should be pretty solid going forward.