({8} magic symbol) ({G} magic symbol) at most, depending on how many creatures you control available.
Steps
Cast Sprout Swarm with buyback by paying ({4} magic symbol) ({G} magic symbol) , reduced by ({1} magic symbol) for each creature you can tap as you cast it.
Each Stormsplitter you control triggers, creating that many token copies of Stormsplitter.
Resolve Sprout Swarm, creating a 1/1 Saproling creature token and returning Sprout Swarm to your hand.
Repeat.
Notes
You should aim to tap as many creatures as possible (up to five) when casting Sprout Swarm to reduce the amount of mana you pay to cast it.