Floor plan design city villa with basement improvement suggestion?

That works wonderfully in theory, but in practice it's nonsense without sauce. Even in non-boom times, it's not advisable for the untrained. Self-awarding contracts is slippery ground for beginners and can turn into a roulette: after the trades A, B, C, and D, you need E, you can't just prioritize the cheapest bidder for U (just because they happen to have time and could even offer a friendly price). If E hasn't worked with D yet, that is very likely to result in a lot of management hours at the connection points. Self-awarding by laymen could be my favorite joke if I were a cynic - but I'm not. When awarding the planning service, you have already clearly missed the mark, if you ask me.

Could it possibly be the same one?
(with all humor, the question is unfortunately serious, as it suggests itself with the brilliant planning)

Sorry, I don't understand the statement... We will plan, coordinate, and award the trades together with the civil engineer and have it double-checked by the TÜV.

However, I don't see self-awarding as rocket science; certainly, the whole thing is much more relaxed with experience. If you have the time for it and stay on top of things, it should work even for laypeople.

Funny, when I was 16, I significantly downsized "in terms of my room" because it was clear that I would be gone in three years anyway – my parents used a move to save 30sqm right away.

A lot has already been written, but I would really consider whether you could downsize a bit more spatially (costs!) and instead build somewhat more sustainably despite larger children's rooms. Instead of 33sqm for the daughter, 20 can also be furnished beautifully with a couch and a dressing corner. It's just a lot of unused space. Have you ever mentally tried furnishing it?

For the son, I would build so that it can really become a granny flat that could theoretically be rented out. So at least connections for a kitchen and not just one big room.

Size alone is not a quality feature and where costs are not irrelevant, the children can live large even with a little less.

I don't see the self-awarding as rocket science either, certainly the whole thing is much more relaxed with experience.

With experience, one is simply no longer subject to the unfounded hope that some brave hero will somehow manage it.

If this is supposed to be a kitchen island ... what do you want to do with it? The room is 326 cm wide, 60 cm kitchen on the left, then at least 2x80 cm passage, leaving 100 cm width for the kitchen island.

Still open ... mini-office and why a proper guest bathroom on the ground floor?

If the terrace is located like this on the ground floor, then half of the basement - son's room has no window. In any case, I think this is not a concept yet. By the way, I also call the bathroom in the basement too narrow. If there has to be an installation wall, then 120 cm room depth is nothing. It should be 140 cm.

A kitchen island would be nice, but as you already mentioned, it probably won’t fit.

The guest bathroom is therefore planned on the ground floor because for cost reasons we only want to prepare the bathroom in the basement, i.e. have the pipes and water lines installed in advance.

If we manage the costs, we would leave out the shower in the guest WC and instead make the office a bit bigger.

A kitchen island would be nice, but it probably won’t fit like you already mentioned.

Really? Guys, guys – this is your house! Once it’s built, it’s too late. So if you want a kitchen island, then plan one in and rebuild the house!

And if someone is supposed to live there in the basement, then there should be a bathroom EXACTLY there and not on the ground floor.