Help needed for improving my texturing workflow

Hi guys. I am pretty much new to texturing and applying materials to my models. I think I have problems in the way I apply materials. For example, this is what I do right now:

1- After the 3D mesh is finished, I make an extrusion wherever I want to have a door or a window for example. I do this because then I can select the interior face of the extrusion and apply to is the window/door material. The problem I am having is that I am getting insane amounts of geometry for simple things, and a lot of tiny materials.

2- After I have all the materials applied I would bake the textures into a single image.

3- Since I am using Blender 2.8, the only choice is Cycles, hence I use a Mapping node and a Texture Coordinate node to align the images inside the faces I want to apply the texture on.

My textures are mostly diffuse, I will see next what do I do with metallic and specular.

How can I improve what I am doing?

Some reference images: