You can accomplish this task using NirCmd by NirSoft. It is generously provided as gratis software from Nir Sofer, the author. It is not currently open-source, but that was not mentioned as a requirement.
You can set the cursor position using the setcursor [X] [Y] command. From the documentation:
Set the position of mouse cursor. The [X] and [Y] ...
AppAudioConfig and SoundVolumeView can help you achieve what you want.
Both are gratis and without any bloat. They are portable except when they need to modify the Windows registry to make the required changes. I have personally used both, and found them to be excellent. As such, I can recommend them.
This a good description of AppAudioConfig: