What you need to know !
The goal is to maximize your handbuff trough both Emissary and Spirit of Rebirth.
But actually, they work quite differently. Spirit push you to have only a few cards in hand to be able to pick which creature buff. On the other hand, Emissary want as much as possible.
From my feeling, Emissary need at least 3 creatures in hand to be worth. Ghost Dragon buff is obviously a big bonus.
What you need to understand also is that Gagana, Zoologist and Bloomsprite are there so you're not depleting your hand by playing them. Just pray for Bloomsprite to give you a creature :)
Most of the time, you'll be playing defensive, as sac need to be answer with pressure.
Agaisnt Burn though, you'll have to play offensive. Zoologist can help you to adapt.
And build lands please. One at a time. You can eventually start to draw when you have 3 forest 1 desert but still, don't do it too much, you need your 6 lands for SE. But 6 turns is most of the time not enough to prep them to be as big so... 1 turn or 2 drawing before reaching the treshold is ok.
Keep your Grovecaller for a really good trade or for Ghost Dragon/Soul Eater shenanigans to face.