You can have a look at the models from the ArchVis example scenes available for UE4 to get a general idea of polycount for Architecture Visualisation.
If you start adding one highpoly object after another to the scene, you’ll surely hit the point where it impacts performance even on new powerfull Hardware.
Going back and rework lots of models to save polygons at this point might be harder then starting from scratch again.
I’d suggest you to do it the other way arround.
Start simple and add detail once you’re sure everything works.
I’d model the basic room shape first, insert placeholders for every major object in the room and then start detailing.
Again i’d start with the rooms itself. Adding stuff like trims and textures.
Then replace objects you know you’ll need a higher polycount for.
But since you said:
you might want to start learning the basics of modelling, uv editing and texturing first before trying to do a project like this.
Set yourself achivable goals, this keeps up the motivation.
Otherwise you might come to a point where you realize that you’ve worked on something for months without any results.
Especially for the purpose of learning, it’s good to keep things simple.
Don’t do overly complicated models with high polycount if you still need to figure out how to model, uv map and texture a model.
It’ll only slow down your learning and increase frustration level.
Once you’re able to do all this with a simple lowpoly object, you’ll be also able to apply it to a model with higher resolution.