Well, ultimately it should still be a bit of your "dream home," even if all the first "dreams" might not seem feasible. Unfortunately, there is no plan to be seen, but maybe you can implement some things later if the "feared" case occurs, such as retrofitting a "standing balcony" or similar solution, if this child-related topic really turns out the way you now believe.
I had a sauna in the house; it’s nice if there is extra space. But with children, space usually tends to be tight in the house, so maybe it could take place later INSIDE the house if you still live there in old age. Until then, I could more easily imagine (as we do) an outdoor sauna. Something like that can be made from a "cheap" DIY garden shed or built yourself at a drastically lower price than an indoor sauna, also because no living space is "wasted." At that time, we bought a used indoor sauna, even in the BB:D area, and placed it in the garden on a concrete slab, screwed a modern formwork on it, built a simple bitumen roof; costs were almost negligible in comparison. Next to it, we had a nice garden shower, and relaxation took place in the living room by the fireplace. Inside the house costs you expensive living space, you have the problem of humidity, and it can never be implemented as simply and rustically as outdoors; all that costs a lot of money.
Just as expensive is the provisioning of guest rooms; here too, the option is to "outsource" them for individual cases, e.g., in a nice garden shed/shepherd’s wagon or similar.
Of course, all this must fit your life, but dreams don’t have to die; maybe it’s enough to redesign/rethink them a bit.
In general, as a former basement owner, I would also give that up if possible, depending on cost/benefit.
Whether the term villa or other designation fits is usually just wordplay; you just have to find the price drivers and look for ways to still enjoy the house. Maybe you have gotten the impression so far that all your wishes are crazy; I don’t believe that. You just have to adapt them so that they fit your budget and your life.
One main point was a guest room that we originally couldn’t cleverly accommodate either on the ground floor or the upper floor.
Just post your whole project along WITH a questionnaire, then maybe it will work without an attic guest room and some dreams can be preserved. :D