I want to build rooms and worlds in VR. Where can I get started?

So. I want to take a 20x20 room and turn it into a world or room in VR or MR. And Would like to test on my Meta Quest 3.
I am looking for the simplest solution to get started where I can use 3d Assets, and materials to build out VR rooms.
I want to turn simple object (e.g: table) in the 20x20 room into a different table or structure.
In the future, I would like to make objects that can be interacted with in the VR world (e.g: Clipboard, etc)

How can I get started. What should I focus on? Any sources for a newbie?
I am current a web programmer so I know the foundations and fundamentals about coding. I am also a designer and I know some about design and 3d programs (sketchup, etc).