Planning a single-family house with 4 children's bedrooms

It would also be relevant to know how old the children are. With almost adult children and latecomers in the baby stage, you might also plan for three children's rooms. I would also recommend going to the architect. If the planning firm is good, they can, for example, estimate how much storage space you actually need – because I see a lot of planned space, which on one hand seems logical with four children, but on the other hand could also be unnecessary. You could also calculate whether a basement would be more sensible to put all the technology, storage space, and housekeeping underground in order not to become too large above ground. Or you could consider whether the parents should move downstairs if they don't want to share the bathroom with the children. For that, an office could go upstairs. We know too little about you to advise well on this.

We actually wanted a plot of about 600 sqm that is around the corner, but it is supposed to cost the same as the 1000 sqm one, so we decided on the larger one. Unfortunately, splitting is not possible; we have already inquired about that.

The budget is not sufficient. You should limit yourselves to a smaller house.

That the seller would not sell the plot in parts is a different matter than if it were not divisible for development reasons. Show both plots. Would the other one around the corner maybe be immediately within the funding area? 1000 sqm x floor area ratio 0.2 would result in 200 sqm buildable area – that could be partially sold off (and increase the budget).