({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.