I myself only had a 10 sqm own room back then in a shared apartment facing northeast. That’s fine for our kids. I think our son will play a lot with us on the ground floor in the first years later.
We also used to have the kids’ rooms smaller and the kids always played in the apartment, e.g. in the large, square hallway. But I then found the 10 sqm from back then too small; I think 12 sqm is okay, although I’d rather sacrifice hallway space. I would also remove the door in the kitchen. The staircase is probably the key issue; we initially wanted a straight staircase but then realized it was just stuck in our heads. It became a quarter-turn staircase, and now that I see it, I don’t miss anything. Besides the shape, I would rather focus on the design style, because such a thing in the middle of a room has a strong effect. Someone once wrote here that the railing mostly defines the appearance of the staircase, so you should make sure to find something stylish. In this respect, I would prefer to spend money on making it a great staircase (materials/look); the shape is secondary for me. The seating window is probably actually born out of lack of space. But if you like it that way and enjoy living with it, I find it stylish. It’s similar with us—we usually sit next to each other and watch the sheep outside while eating; however, we no longer have children living with us. The technical room can work like that… maybe, but then nothing must go wrong; better a bit bigger. We have 7 sqm and that’s sometimes a tight fit with photovoltaics, controlled ventilation, etc. Every trade demands space there—from telecom to water connection… Careful planning (or having it planned) is necessary! We wanted to place a 2 m tall shelf there, but now it’s only 80 cm wide due to the electric cabinet, etc. Everything turned out wider/different than neatly drawn in the plan. Additionally, there are one or two waste/ventilation pipes, etc.; maybe it was just a problem of our rough-and-ready planner.
Do you all watch TV on the couch in your pajamas? I wear jogging pants and a T-shirt there. With the gangster teenagers nowadays, depending on the jogging pants, you’re probably seen as cool rather than embarrassing…
Best is to fall asleep once in just your ribbed underwear and a beer bottle in front of the TV watching western movies when the teenagers come to visit. Then the problem is solved for the future. There will surely be more suitable locations then. I like your tendency toward the rather minimalist; I have parted with many things, my wife struggles more with that. I think you should discuss clearly beforehand that you want to live that way in the future. Then it also works with much less. It’s stupid only if you realize later that you haven’t considered it consistently enough; generally, however, I find it good. I also like that you—without seeming stubborn—want to implement some things differently even if “people” usually do it another way, like the seating options at the dining table. I’m already curious how it will develop.