Minimum floor area - utility room and AZ on the ground floor - without basement

So you at least don't have to worry about that with standard goods.

No, you do not not have to, but you must not even. Because if you do worry and end up with a different heater, then the washing machine might have to be placed elsewhere, otherwise there would be too little clearance space in front of the fuse box.

With knee problems, I would choose a podium staircase. After all, you then have a bit of a "breather" after 8-9 steps. This type of staircase is also much more compact, both on the ground floor and the upper floor. Under the upper flight, you can easily create a small storage room.