I would start with Unreal Engine 5 fundamental tutorials, such as material and how to navigate the user interface.
Then focus on importing your Revit scene using Datasmith and Dataprep tutorials.
After that, I would look into lighting tutorials and rendering turtorials.
All can be searched on YouTube.
That is all based on you my friend. To get it up and running from scratch, with zero experience, I would say no more than a week to watch videos and then trying to import an existing Revit model to have something working.
But once you have your systems in place, and you are familiar with how everything works, then starting a new project would take less than an hour.
In addition, you will likely be adding more functionality as you go with each new project. So it’s an ongoing process.
Yes, and you should most definitely create a template to keep consistency amongst projects and efficiency in project setup.
Also, I highly recommend creating a separate project that is used as your asset library to hold all of your materials and blueprints.
I have a short explainer post on how to accomplish this using symbolic links on windows systems here:
[UE5] Use of Windows symlinks to placeholder UAssets in a different project? - Development / Programming & Scripting - Epic Developer Community Forums (unrealengine.com)
You can do that using Dataprep on import where you run a “recipe” on the imported assets. Or, you could create material functions that allow you to swap colors.
Adding the ability to open a door can be done in blueprints that you recycle by simply dragging and dropping onto a door.
Again…you will need to do your homework to learn the techniques. But the information is out there for free.