How I can do several scenes with transition from each to other

Hi I need help!
I have some problem … I need to do multiple scenes with transitions from one to another.
First, I will have an intro scene. From which you go to another scene (something like a hall). And from it you can get into other scene (like a room).

How could I make these animated transitions?

Should I have only one main scene in which I will change sub-scenes (intro, hall, etc.)?

Or I have to make a own scene for each entity and change it to a straight line in the renderer?

Or it is not necessary to create scenes for each entity. And would be better to combine them into groups and add / remove them to the one scene?

Should I have only one renderes or I need own renderer for each scene?

Or is there another way?

This example on the official site may help you.
It show how to render multiple scene with setScissorTest transition.
It require two scenes, but only one canvas renderer.

https://threejs.org/examples/?q=scene#webgl_multiple_scenes_comparison