I would suggest you be sure to have Stream-based APIs for Storage so it integrates well with other .NET APIs and third-party libraries .
You should also have async/coroutine/whatever methods for reading/writing storage, since it looks like the ones you shared are synchronous. If they are called on the game loop thread (I assume any game scripts you write run there by default) with large files, you could get frame drops. Adding async variants will make the calls more complex (you start calling on one frame but finish on another) but developers can use this to minimize stutter.