I like the mechanic of having a fixed number of stars. I think it falls apart having to run around picking them up again, or being -1 star when it gets stuck in an unreachable area. To fix this, I think a long reload animation which magnetically pulls in stars would be nice. The duration of the animation should depend on how far away the stars are. I would replace the "pickup range" stat with "pickup speed" as well to let players upgrade how quickly the stars return after being thrown. This also adds the potential for as a unique joker, doing damage to enemies when a star is removed.
This would likely also require some changes to the boomerang to ensure it stays different enough from the stars.