ᐅ Single-family house floor plan, approximately 200 sqm – comments welcome

Dear forum,

After spending hours as silent readers in this forum, my partner and I are now ready to share our floor plan for your feedback.

First, here is the questionnaire:

Development Plan/Restrictions
Plot size: 1322 sqm (approx. 14,230 sq ft); about 23 x 56 m (75 x 184 ft)
Slope: No
Site coverage ratio: no development plan – § 34 Federal Building Code
Floor area ratio: no development plan – § 34 Federal Building Code
Building envelope, building line, and boundary: no development plan – § 34 Federal Building Code
Edge development: No, only carport/garage and garden shed or storage shed allowed
Number of parking spaces: no development plan – § 34 Federal Building Code
Number of stories: no development plan – § 34 Federal Building Code
Roof style: no development plan – § 34 Federal Building Code
Design style: no development plan – § 34 Federal Building Code
Orientation: corner plot approx. 23 x 56 m, streets to the north and west
Maximum height/restrictions: no development plan – § 34 Federal Building Code
Other requirements: none

Client Requirements
Design style, roof type, building type: Modern but not too "clean"; preferably a gable roof with a shallow pitch (20–25°)
Basement, stories: no basement, preferably 2 full floors
Number of occupants, ages: currently 2 (30 and 31 years old), planning for 2 children
Space requirements ground floor, upper floor: Ground floor: entrance hall + cloakroom, guest toilet, office/guest room, large utility room + pantry, open living/dining/kitchen area, approx. 100–110 sqm (1076–1184 sq ft);
Upper floor: 2 children's rooms, children's bathroom, open "parents’ area" with dressing room and master bath, small storage room, preferably gallery/open space, approx. 90 sqm (969 sq ft)
Office: occasional home office use, combined workspace and guest room
Overnight guests per year: 10 nights
Open or closed architecture: open
Conservative or modern construction: modern, not too "clean"
Open kitchen, kitchen island: open kitchen with freestanding island; slight separation between dining and living areas desired
Number of dining seats: 8
Fireplace: yes
Music/stereo wall: no
Balcony, roof terrace: no
Garage, carport: double carport
Other wishes/special features/daily routine, also reasons why something should or should not be included: if possible, an open staircase

House design
Who designed it: DIY based on various sources
What do you particularly like? Why?: Separation of dining and living areas despite open layout; direct passage from carport into utility room/pantry and then the kitchen; open space with view of the garden; all bedrooms facing the garden; rectangular building shape
What do you dislike? Why?: -
Price estimate according to architect/planner: floor plans of comparable size were around €450,000
Personal budget limit for the house, including fittings: €550,000–580,000 including carport, excluding landscaping (plot already owned)
Preferred heating system: ground source heat pump, KFW 55 standard

If you have to give up something, on which features/extensions
-you can give up: open staircase; storage room upstairs; fireplace
-you cannot give up: all other rooms in some form

Why is the design as it is now?
A mix of many examples. So far, the floor plans we received from planners were less to our liking.

What is the most important/basic question about the floor plan in 130 characters? Affordable (in Lower Saxony; urban area)? Can the staircase on the upper floor be built as shown? Does a ventilation system make sense for KFW 55?

Please ignore the window placement for now; it is rather arbitrary at the moment. The house will be positioned with a 3 m (10 ft) setback on the northeast side of the plot. This means the garden will extend to the south (short side, approx. 23 m (75 ft) total width) and west (approx. 56 m (184 ft) length).

Suggestions, comments, and improvement ideas are very welcome.

Many thanks in advance and best regards,
Carlotta