How deep should the stair landing be? How to design it?

My favorite for the wardrobe furniture is so far as outlined in the attachment.

The window in the back wall can be easily moved to the east side.

I would prefer not to place the toilet on the other side of the stairs; in the worst-case scenario (care case), one could sacrifice the wardrobe in the current plan and set up a bathroom on the ground floor.

Hmm .. I find that narrow and uncomfortable. And the green part is probably not even deep enough for rails. Are children taken into account? And, you can also create an opportunity with a shower from the guest WC here: Just build a shower bump to the left into the living area.

The niche depth is already on my list of questions for the next appointment. The seating is meant to go there for tying shoes, not for a cozy chat. Since our apartment hallway has almost the same dimensions as the wardrobe area next to the WC, I can already imagine the design possibilities quite well.

As you already say, there would then be a bulge in the living room - that is out of the question for me.

I don't find 150 cm in less than 60 cm depth very generous for a real family wardrobe. For me, that also includes bags, hats, scarves, and gloves. And, I don't know if one should overestimate the situation of suddenly needing a shower in the guest bathroom. See also one of the currently ongoing threads.

That's why I actually didn't want to post the floor plan... :-(

We have certainly put a lot of thought into it and planned with a "cloakroom" from the beginning – that should be more than in many other floor plans I've seen here.
I understand pointing out that 1 m of cloakroom for jackets AND shoes is too little. But not when you can easily accommodate 1.5 m each for jackets, shoes, and scarves/small items, sometimes even ceiling-high.

Regarding care, I have definitely formed my own opinion. Not least because I have experienced care in the family.

Well, the hallway seems too narrow to you .. how can one judge something if they don't see the floor plan. You just notice different points of emphasis.