Point 6:
Are the floor-to-ceiling windows on the upper floor okay? Or is there too little light?
Would a regular window be better? What is actually normal? I mean, what size?
⅛ of the floor area is the rule; so everything is fine.
I have a completely different opinion. Strangely, I wanted to write yesterday but forgot, and today I searched for this thread with this house with the floor-to-ceiling windows on the upper floor and couldn’t find it until Bauexperte replied.
I do know the 1/8 rule, and it may also apply for diffuse light.
But from my own experience and a training subject in optics and light theory I learned:
through a slit of about 80 - 90 cm never can come as much radiation as from a wider opening of about 160 or 180 cm.
Here I also like to compare a narrow floor-to-ceiling window with a sill window
regarding direct sunlight.
A room is usually wider than it is tall, so you should also let the light in through the width of the room. Additionally, there are the reflecting surfaces like walls or floors: a floor getting light through a floor-to-ceiling window will very likely reflect less light due to color and structure (namely not smooth white) than a (slanted) wall that you paint white. Besides that, sooner or later you will probably place something in front of these floor-to-ceiling windows.
You want to brighten a room that is 420 cm wide, the slope can be neglected here... also it is a west-facing window, which in winter hardly receives any solar radiation... so I would go wider with the windows.
Just for illustration, I hope it is enough and understandable what I want to say...
For the summer one can demonstrate it more clearly if the arrows in the plan are drawn horizontally, i.e. coming from the west.
I’ll give a tip: go once or twice to a model house (there is always one or two nearby somewhere) and look at these classic rooms under the slope with these narrow windows on top