ᐅ Floor Plan Design for a Semi-Detached House 17x10 m – Optimal Use of Space?

Hello everyone,
I’ve been following the forum for a while and have been pondering over a practical floor plan for our semi-detached house project, but I just can’t make progress. The maximum allowed footprint for each half of the semi-detached house is 8.50m (28 feet) wide by 10m (33 feet) deep, so we don’t have to build a “narrow” house. If possible, we want a staircase with straight steps, either straight or a half-turn landing staircase (I simply can’t stand the steps that narrow towards the middle and don’t want to walk on that for the next 20 years...). The “standard” semi-detached floor plan with guest bathroom, cloakroom, spiral staircase one behind the other and then living area etc. doesn’t appeal to us at all. We’re not necessarily looking for fancy features that take up unnecessary space but want the “perfect” layout with a bit of flair. As a layperson, I’ve been stuck on this for weeks—whenever I think I solved the ground floor, the upper floor doesn’t fit and vice versa. So I’m hoping for your input.
We already own the plot, and the plan is to rent out one half of the semi-detached house and live in the other. That means we will build one showpiece and one with decent standard; the exterior should be uniform.
I’ll just start:

Development plan / restrictions
Plot size: 479 sqm (5158 sq ft), 23m (75 ft) wide, 20.80m (68 ft) deep
Slope: slight incline towards southwest, about 1.50m (5 ft) max over the plot depth and width
Floor area ratio (FAR): 0.35
Floor space index (FSI): 0.7
Building line / boundary: 3m (10 ft) setback line (not including garages etc.), no defined building envelope
Edge development: no (garage allowed)
Parking spaces: 2 per unit, total 4
Number of floors: 2 full stories
Roof type: pitch 25–45 degrees, gable, half-hipped, vaulted
Style:
Orientation:
Maximum height / limits: max. building height 9.50m (31 ft)
Additional requirements: none

Homeowners’ requirements
Style, roof, building type: modern, clean lines, simple building shape, gable roof
Basement, floors: basement preferred, 2 full stories, attic as expansion reserve
Number of occupants, ages: 3 (45/40/2); the second half of the semi-detached house should be suitable for a family with 2 children
Space needs, ground and upper floors:
Ground floor: guest toilet, cloakroom, large open living/dining area, open kitchen
Upper floor: large children’s room, master bedroom, family bathroom, possibly small study for home office
Attic (expansion reserve): studio / guest room / hobby room, connections/drywall for shower bathroom
Office use: family use and home office
Overnight guests per year: about 20 nights, 1-4 persons
Open or closed architecture: mixed—living/dining/kitchen open, stairs to basement and attic closed, no direct access to upper floor from living area
Traditional or modern construction: modern
Open kitchen, kitchen island: both
Number of dining seats: 8
Fireplace: yes, if within budget
Music/speaker wall: no
Balcony, roof terrace: no
Garage, carport: no, 2 parking spaces
Utility garden, greenhouse: no
Other wishes / special features / daily routine, including reasons why certain things should or shouldn’t be:
The attic should be finished by ourselves. If the basement doesn’t fit the budget, a utility room must be planned on the ground floor; however, due to the slope, we prefer to invest in the basement. The family bathroom should ideally have a T-layout with a level-access shower and toilets “back to back.” Walk-in closet in the master bedroom is desirable but not a must; if not possible, at least 3m (10 ft), preferably 3.50m (11.5 ft) for wardrobes.

House design
Designer: architect from a construction company
What do you like most? Why?
- the opposite entrances
- the straight staircase
- the kitchen/dining layout
- glass wall with door to separate hallway and kitchen in the design of the semi-detached house on the upper plan side
What do you dislike? Why?
- planned without basement; if including basement, the stairs are located between kitchen and dining area (going all the way through the house); with basement, utility room could be omitted
- staircase too much “in the middle” — I would prefer it shifted slightly to the right side of the plan to gain more living space
- 4 to 4.5m (13–15 feet) window front with sliding door to the garden desired instead of regular doors to better open living space to the garden
- semi-detached units are not offset in height relative to each other (this was a request to avoid an overly massive-looking building and to reduce the need for extensive land grading in the southern half—the natural slope should easily allow a staggered design)
- maximum width of 8.50m (28 feet) per semi-detached unit is not fully utilized (only 7.75m (25 feet))
- upper floor bathroom too small / poor layout
Estimated price according to architect/planner: to come (currently company holiday)
Personal price limit for the house, including fixtures: 700k
Preferred heating system: preferably geothermal, if budget allows

If you had to give up something, which details/expansions could you forgo?
- can give up: straight staircase, geothermal, attic expansion reserve (in that case, the upper floor layout would need to change significantly as guest room and one staircase would no longer be needed), T-bathroom
- cannot give up: basement

Why was the design created as it is now? For example:
Standard design from planner? We still need to discuss that; we received the plans shortly before the construction company’s holiday started.
Which requests from you were implemented by the architect? Straight staircase, maximum privacy from neighbors, not a standard cookie-cutter floor plan.
What do you think makes it particularly good or bad? As a layperson, I don’t feel qualified to call it “good” or “bad.” I can only say what I like or dislike, which I have mostly summarized above. We basically like the draft and think it could work with the proper modifications.

What is the most important fundamental question about the floor plan in 130 characters?
Would changing the staircase but keeping the entrance arrangement significantly gain living space, and would basement and attic alter the layout?