South-facing plot 700 sqm, single-family house approx. 150 sqm, any ideas or input?

Whatever may distinguish the elevation point classes O, X, and I from each other: the slope of the property apparently concentrates fully north-south, while it is practically flat in the west-east direction. From this follows the recommendation to position the buildings as much as possible along the west-east axis – that is, rotated 90° compared to the model house in the development plan / exposé – and to place the garage as close as possible to the north street. I also did not understand the "building window within the building window," which, however, does not even apply to the model house (?)

I also believe, and have myself most recently decided this way for that reason, that the rectangle represents by far the more suitable house form.

On a slope, the primary ideal is the congruence of contour lines and house axis. Apart from that, the most favorable basic shape is the rectangle close to a square (about 5:4, as many Bavarian development plans also specify) with the entrance on the eaves side in the middle third of the width.

The idea that one has to walk a few meters from the car to the front door sometimes triggers such a great fright that people become blind to the overall solution.

Pinterest, Insta, YT, they basically only show me what is depicted and done in large quantities, but not what is unique or special.
And thus, uniform mush is built. Taste no longer comes from within oneself.

The picture catalogs show, besides mainstream mush, not least many ideas that do not fit the individual property without distortion to the point of unrecognizability. 08/15 or 7016 guarantee the design’s majority acceptance within the circle of acquaintances, and the drive-in single-family home "protects" from neighbors greeting when coming home or leaving. This is apparently important to a generation of builders who already preferred to text their buddy on the schoolyard instead of walking the eight meters to him.

If the principle fits, then the iterative adjustment starts,

But please as a verbal discussion plus rough sketches in performance phase 2 and no further after the resting period of the dough. And also not with the goal of one hundred percent accuracy, which has no business yet in the preliminary draft. One (1!) preliminary draft, discussion, if applicable a second preliminary draft, after the iteration of one of the two then the resting period of the dough – no infinite monkey doodling to exhaustion!
During the resting period of the dough, then set the course, and with these insights then the discussion whether the previous preliminary draft should be further developed or an "answer to question 2" alternative draft should be adjusted.

go to Google Search and always find the same thing

Good tip! Search for images everywhere and not just in digital image databases, also in architecture and home magazines, take screenshots of movie scenes or photos of TV stills, take photos when you see something, cut something out of a newspaper… Print out what is digital and create the mood board with scissors, cardboard, and glue. The physical engagement and selecting what can go on the board is extremely helpful. The result says a lot about you and the house is supposed to be for you.

The image catalogs show, besides mainstream mush, not least many ideas that don’t fit your own land without distorting them beyond recognition.

Forget model home catalogs.

Search for pictures everywhere and not only in digital image databases, also in architecture and home magazines, take screenshots of film scenes or photos of TV stills,

You would need several winning lottery tickets just for the Tatort villas of a single season of Rosenheim Cops.

Forget model house catalogs.

Model houses are at least more realistic compared to the above regarding the land requirement that an average single-family house (S, not S/D) plot can satisfy. Sometimes you can even find feasible examples for 500 sqm plots. At least theoretically. Practically, I fully advise against loading yourself up with role models at all. There are so many possibilities to individualize house designs that even for Müllermeierschulzes with a rectangular floor plan, the "risk" of ending up with an indistinguishable house can be reduced to almost zero. Many "tricks" for that are even exceptionally inexpensive, starting with the omission of 7016; it continues with not just choosing between full facing brick and no facing brick at all.

First of all, thank you very much for the many answers and input for the planning. The tips have already shown us a somewhat different way of proceeding than we have gone so far.

however, I can't make sense of the measurements. Below and to the right go 22.5 and 25.5.. but that doesn't add up to 700sqm.
It is also a bit blurry, so one has to guess whether 5mm is one meter or another measure, e.g. 2 cm = 10 meters.

There was a mistake there.
The plot is 25.4 x 22.8m = 572sqm (to the northwest there is a rounding).
I actually wrote the height measurements somewhat confusingly.
I have uploaded a new one again. Dimensions e.g. 100 = 10m, height measurements e.g. 70 = 70cm below zero point.
But as you already mentioned, one can say that the ground basically only slopes from north to south.
On the NS axis
e.g. border 19cm, 5m = 58cm, 10m = 155cm

Whether one plans a basement, a residential basement, a garage in the basement, a double garage next to the house or something similar then still depends on the BUDGET. So how high is the budget for the house, exterior facilities and incidental building costs? You can eliminate some options if the budget does not allow a lot.

Budget still open about 500-550
Our first idea was initially to accommodate everything in one building to save costs. That is, basement garage, ground floor and upper floor house.
We assumed that it makes sense to build a basement on this slope. Just as a storage space costs and the basement is too expensive due to the budget.

An alternative idea from us would be to go about ~40 more with the basement so that windows can be placed on the east, south and west side in the basement. Use the basement as the actual upper floor (sleeping area) + entrance in the north to the living area (kitchen + living etc.) so we would save the upper floor but would still need a storage area for the vehicles.

What I wonder: what is the legend for the drawn lines? I see two building envelopes?

Black dashed line = building boundary
Brown dashed box with GA = location for garages

Model houses catalogs, Instagram etc. have so far just been our biggest sources of ideas. Otherwise, we have driven around some settlements and got ideas from them.

The opinion about aspect ratios like 5:4 we think is very good. We simply took 10x10 as a starting plan, staked it out on the building plot so we could imagine how big the house will be approximately and how much space is still around it.

.. the uploading probably didn't work, at least I don't see anything.

The opinion of a square ratio, e.g. 5:4, we consider very good. We simply took 10x10 as a start plan and staked it out on the building ground so that we could get an idea of how big the house would approximately be and how much space is left around it.

I take 8 x 12 m for demonstration staking, which can then be rotated by 90° (which is pointless for 10 x 10 m) and you immediately see the difference between with the contour lines and across them. You want 150 sqm, which require a floor area of 125 sqm ("one-and-a-half-story") or almost 95 sqm ("town villa") — in 5:4 about 8.70 x 11 m. From a house depth of 8.70 m, according to the 11ant basement rule, not quite 45% "per basement" votes would follow.

Our first idea was initially to accommodate everything in one building in order to save costs. In other words, basement garage, ground floor and upper floor house. We assumed that it makes sense to build a basement on this slope. Just as storage space, the basement costs, but due to the budget it is too much. An alternative idea from us would be to go about ~40 cm higher with the basement so that windows can be placed on the east, south and west sides. Use the basement as the actual upper floor (sleeping area).

Alone because the driveway to an underground garage also needs length to moderate the height (and not less for a residential basement), I recommend a classic basement (not like today modern under a terrain-level ground floor on the hill side, but under a raised ground floor). Many development plans play only moderately with this by limiting the finished floor level of the ground floor to 0.5 m above the road edge (or similar).