Unfortunately I don't believe that the creator will update the file. There are comments posted now 3 months ago reporting the bugs, and the creator has not responded to any of them, so it looks like the project has been abandoned.
For now the plane is okay for taking screenshots etc, but is, like you said, unflyable, and can't be used for full flights.
I would recommend waiting for a payware Dash 8 to be released. I'm not aware of any projects in development at the moment, but hopefully one is eventually made. As a plus a payware version would most likely have a real Dash 8 cockpit, instead of the CJ4.