As shown below, I have finished modeling my modular building kit. I decided to make most pieces on a single meter width basis, like the wall segments, the floor, and the door and window segments. Each of these can be lined up next to each other. So an 8 meter long wall can include a door piece, a window piece, and wall pieces. Outlets and light switches can also be added on as shown.

I also made some basic kitchen cabinet models here. And the closet model stands out, having a 3 meter length. I thought this was important to make the sliding door closet that I had in mind, and I think it fits well in the space allotted.