starting at level 3 should be ok I suppose, usually you start at level 1 for Star Once Fallen. Star Once Fallen is also a learn by play module, so if you use the rules inside of that module they aren’t the full rules, but I think you are using some… special rules anyways based on the sheet. It’s a little confusing at first.
Have you seen the heromuster sheet as well. I see this is perhaps nice b/c it as multiple PCs on it, but have you done a lot of homebrew stuff for this? Usually, when first trying a system, it’s recommended to play with it as is so you can see how everything works, then start to homebrew or modify a few things.
Depending on how you are using Star Once Fallen, you might check out this thread: Question: Is there an updated "a Star once fallen" to the newest rule set?
HOWEVER, if you are just using it for the story, and running the rules straight from the website (the full Core Rules), then you don’t need to worry about that post above.