Before we tackle the kitchen in the next section, let's place fixtures in the downstairs half bath and laundry.
Our plan looks like this:
We have about 4' of width for our half bath, and our laundry room has a door to the outside, eliminating much of the space. That's OK, because now we have a place where kids can take off their shoes (as if they would actually comply) before coming into the house. It's a good idea, anyway.
But, I have an idea, which I will show, below.
I narrowed the "throat" of the half bath and placed a jog in the wall between the laundry and the bath. I also turned the door around, but either direction would be OK. The back wall of the laundry was narrowed by 6" to make more room for the bath, but now we have an alcove in the laundry room where we can put a shelf, if we like. I also placed a small window in the bath, setting the height to 30" and the width to 24". We could go smaller, if we like.
Now, let's place a toilet in front of our window, and a small, wall-mounted sink next to it. While we're at it, let's find the washer and dryer in the Fixtures library, and put one of each in the laundry room. We might also consider a window for this room, as well. Personally, I like placing a window in the right-hand wall of the laundry, so it overlooks the patio outside. This would also permit shelving above the washer and dryer, for such things as detergents, fabric softeners, etc.
Depending on the default material for appliances and fixtures, you might want to change the color of the items to something like White (Shiny), since that is a very common color for these types of appliances.
Now, our plan looks like this:
I made just enough room in the bath to have the toilet and sink next to each other. There is plenty of space for the washer and dryer, and the right-hand wall has enough space for a "regular" window.
I could do some detailing (shelves, etc.), but more important tasks await us, so let's move on to the next section: The Kitchen. The kitchen is, of course, by far the most complex and detailed part of the entire house.