ᐅ Planning a single-family house with 210 sqm of living space, without a basement

Hello,
we have made some initial fundamental decisions, drafted a basic plan, and are seeking constructive feedback.

Zoning Plan / Restrictions
Plot size 800 sqm (8,611 sq ft)
Single-story ground level, building area 180 sqm (1,938 sq ft), 18x13 m (59x43 ft) building field, 25° roof pitch, gable roof

Client Requirements
Style: modern, 2 full floors with open roof concept, no basement, 2 bay windows that become roof terraces above, high ceiling heights (at least 2.70 m (8 ft 10 in) on the lower floor, open upstairs with up to 6 m (20 ft) wall height, 9 m (30 ft) ridge height possible), total living area approx. 210 sqm (2,260 sq ft).
Planned for 4 people
Office: rarely used for home office
No overnight guests per year
Open kitchen with cooking island
Number of dining seats: 8
Fireplace
Double prefabricated garage located away from the house with a small adjoining storage room, garden shed for storage

House Design
Planner: mix of model home + do-it-yourself + planner input

What do you especially like? East and west roof terraces (sunset views), large open dining/living/kitchen area, orientation according to cardinal directions, fireplace in the room, view of the staircase as a highlight, south side with external blinds, 3 doors (2 sliding, 1 standard) to the south terrace, separate parents’ area with sauna, niche in the hallway for coat storage

What don’t you like?
Children's rooms possibly too small at 12-13 sqm (130-140 sq ft). However, planning includes potentially adding a gallery in 10 years once the kids are old enough, which could create additional space. The gallery could then be used as a play or sleeping area. Considering possibly extending the house by 1 m (3 ft) and reducing the size of the bay windows; this would provide more room for the children if necessary. Alternatively, the upstairs hallway could be reduced? Personally, 10 sqm (108 sq ft) was more than enough space for me back then.

Wall thicknesses were considered in the square meter calculations (only the staircase has not yet been deducted/calculated out).

Cost estimate and personal budget excluding landscaping, plot, and additional expenses: €600,000–650,000 (approximately 600-650 thousand euros). An additional approximate €100,000 is budgeted for extra costs, furniture, and landscaping.