Floor plan & orientation of house on a 420m² plot

Referred to what?

You achieved that with just under 200 sqm. Without incidental building costs or ancillary facilities.

Do you have a second floor area ratio for ancillary facilities? If not, then you are allowed to build 170 sqm.
The house is just under 130 sqm. That leaves 40 sqm for terrace, paths, and parking spaces.

About the design itself: there are already some big blunders in it. Bottleneck next to the staircase landing, guest WC too small for this furnishing, kitchen not functioning due to lack of workspace or storage. For that, the TV distance to the sofa is over 5 meters.
Upstairs it doesn’t work at all with what you have drawn. You split the long 13 meter wall for bathroom and bedroom with dressing area.
And the exterior views frankly don’t make sense either. Floor-to-ceiling windows are nice, window bands are nice – but you don’t have to plaster everything over or overdo it. Especially because you should also use gables. By the way, a house should smile at the front if you look at the facade with imagination. What expression do you see in the east?
The three window bands next to each other look totally negative… they are just three minus signs…
If the neighbor gets too close because the plot is small, at least balustrades upstairs should provide privacy.

What I want to praise, however, is the old school variant with which you drew. It has advantages, namely concentrating on the design and not on foreign software. And you dare to erase.

No, we don’t have that, so I assume 170 sqm like you.

because then the plot is basically too small for "everything".

I suppose the plot is already there. So rather everything is planned too generously on it.

Then you also have to plan with 170 sqm. As already said, this also includes the paths.
I wouldn’t draw anything until this is clarified, because otherwise the plot is basically too small for "everything."
Honestly, I can’t imagine that the second floor area ratio is not possible.
Therefore, get a professional who can read and implement the development plan.

Yes, you have too little storage space. But that should be planned right from the start in the design; it is a process as well as a preliminary consideration and weighing, and is not added afterward.
A standard 08/15 design for 650 sqm ground area does not fit on a 420 sqm plot.
If you want to plan garden-optimized, then you do the entire development from the north side from the garage side and include the east in the garden planning as well as a small attic for the (subsequent) expansion for office rooms and storage space.
In my opinion, you have to make some compromises in the overall concept. But as I said: this belongs in professional hands, and then the design can be discussed here as well.