Thank you!The demo comes with the free version of the plugin which does not have as many features but still works. The paid (premium) version of the plugin can be found at itch io.
I dont think any of the stuff you mentioned is possible in either version of the plugin, though. Skyboxes are supposed to be a thing in the premium version of the plugin but I think they might be full of bugs. If I am on map 1 and setup a skybox, it might work, but if i go to a different map the skybox stops working, renders whatever it want, does not update, and often behaves like any normal parallax background. Seems that changing to another map messes up skyboxes. I wonder if skyboxes are still a work in progress or what. Lets see what @Dread_Nyanak says.