Floor plan for 137m^2 bungalow optimization

I find the idea of building the house solely with equity fundamentally interesting - but not for Deone’s situation. In your case, however, I would start thinking about it from scratch again - it is still possible and take your time planning the whole thing! You are young, that’s nice. You think ahead but in my opinion you skip huge and crucial periods of time by immediately landing in retirement, which you perhaps imagine as being disabled, etc. Ok, all that can happen but - you lucky one - you still have so much time until then and so many things will happen/change that you just can’t plan for. 40 years!!! Life will be completely different! I would definitely allow myself the square meters I need to live my life WELL WITH my family, I think that would be at least 150-160sqm. Your children will grow older, perhaps they won’t get along, bring friends over, have urgent needs, the mother’s life changes, professional/health changes and much more. All that can happen before you reach the age you are already thinking of now. And then someday you’re old and... plop... everything is different, meaning you built the house 40 years ago and maybe didn’t implement things because of that, which now don’t fit at all. My tip: do NOT plan for old age now, if something happens in between you will have to decide according to the situation anyway. With two children... who knows what Mother Nature still has in store :D ... I would definitely have a second bathroom/shower in the house, without a guest toilet at all. And... you also want to have peace from each other sometimes (sounds unromantic but is often realistic). We’ve gone through this once in life with a house and children who grow up and change, with parents in the house etc. and therefore I would strongly advise you to take out some money and allow yourself the space/comfort that you NEED NOW and definitely in the coming years in order to live nicely, sometimes with guests as well. And... I’m not talking about fancy stuff and technical gadgets, but really just living space and sensible equipment. At the current interest rate level that’s no problem, your situation is excellent, I would definitely not torture myself. So - back to square one and think anew!

You can't do without: air heat pump, covered terrace,

I have created something here without the covered terrace.

Why? In the first post you write that you can’t do without a covered terrace.

We don’t need a "storage room" for food

Nobody writes that either. But you need storage space, and that near where activities take place.

I personally don’t find the walk-in closet bad to use as a passage to the bedroom.

Basically it isn’t. But squeezing a desk, a shelf, and wardrobes into 9 or 10 sqm won’t come close to doing justice to any of them functionally. Also, clothes cause dust.

Your two drafts are not senior-friendly anyway because of the passage rooms and long distances... The toilet could be closer to the bedroom, not only in old age.
I would definitely advise against self-creations – basics that are necessary for house planning are missing.

Suggestion

go crazy, both children's rooms with loft beds in the attic with pirate stairs, open space with a view up to the roof, gallery into the attic, Märklin/Lego room in the attic, suitcase+decor+ski+surfboard corner, I'm missing the 3rd dimension, which you will build expensively anyway

I like it. It reminds me of my bungalow ideas. I also still have one saved on my home computer inpetto - related to the Scanhaus Marlow Marlow 147 B, but with a narrow staircase to the attic for storage space for suitcases, decorations, and seasonal clothing plus a hobby room.
Storage space is totally missing here with the OP. Maybe that's because at 27 you haven't really acquired such things yet.

So, I’m reading a lot of ideas here that I haven’t even thought about yet. I need to give that some thought. We can take out a loan, but we’d prefer not to. But well, if it comes down to that, then so be it and it wouldn’t be that bad. I’m attaching the plot of land here. There is no development plan, but the 3M boundaries to the neighbor must be observed. The garage may be built on the property line. In the picture, you see a tractor on the property, so don’t be confused by that.

Why? In the first post you write that you can’t do without a covered terrace.

That’s why I’m writing, maybe instead of the covered terrace, a pavilion as a replacement. It doesn’t have to be the covered terrace urgently, we just want to have something where we can sit outside even when it’s raining.