Floor plan improvement suggestions for a single-family house on a south-facing slope

I don’t know. You seem to have informed yourself well, but the leap from a hobby or small side business to a commercial enterprise comes with a completely different set of regulations and requirements. If I remember the operational and workplace regulations from my apprenticeship, then I don’t see how you could get approval for a commercial business in a converted residential basement. The regulations for extraction systems for wood dust and solvents alone are no joke and require, for example, high air exchange rates and corresponding technical installations. The electrical work is also a whole different ballgame in terms of effort. Then there are fire protection systems, which you can’t just retrofit easily either. There are reasons why carpentry shops close because they cannot economically finance the required operational conditions. Extraction systems also tend to be low-frequency; you don’t want the vibrations of the machines spreading throughout the house either. That won’t be a cheap basement if you want to use the rooms as a business premises. We’re talking ceiling heights of 2.60 m and practically new workshop construction. I can already see the first 150,000 euros flowing just into the basement.

That is simply not correct. It is 74 cm. If you are not sure, you are welcome to ask for a dimensioned version before misleading other people with such claims.

I have dimensioned the house. However, I used a load-bearing wall (24 cm in ridge direction). And we are already in the sketch area here, then plaster and the masons' finishing take away 10 cm from you already in the shell construction.

but nothing really tangible comes from you.

No, it doesn't have to. I am not active in drawing financially more or less unrealistic dream houses, nor with users who do not recognize the flaws in their design, even if they are shown over and over again.
Financially and three stories hardly possible – that bounces off!
Then there are still open questions for you. That shows that you do not really engage with the constructive criticism. In addition, you give explanations that are not represented at all in the drawing. You do not address this at all except for numerous justifications. The love for the self-drawn house is too great to even make an effort as an outsider or tip giver.

After the load-bearing walls in the basement come the ground floor, then the upper floor adjusts accordingly.

That sounds like the perfect recipe for a disastrous upper floor.

Maybe our @11ant will remember the thread where we had a city villa on a slope with a garage next to it. I only remember that the stairs went pretty straight towards the kitchen and the room under the garage – wasn’t there a fitness room in there? Upstairs the children's rooms and the bedroom. But maybe I’m mixing up several designs. In any case, I thought the final result was quite successful and you could probably pick up a few ideas from it.

Nothing rings a bell for me right now.

I ask again, where is the construction taking place? Do you intend to do the carpentry work yourself? At least the workshop suggests that.

I also do not see the ground-level exit from the workshop in your plan. Nor the load-bearing supports. You are aware that your project requires significant structural calculations and corresponding amounts of reinforcement steel. The basement will probably cost around 150k. Here we are back to the budget. 150 sqm living space * 3000 euros = 450,000 + 50,000 garage + 150,000 basement + outdoor facilities 50,000 = 700,000. Presumably, a separate workshop is the cheaper solution.

What kinds of businesses are in the neighborhood? A nail salon is different from metal or wood processing. Be sure to clarify whether you are allowed to operate the business there. How do you want to bring the material from the street into the workshop? Do you never want to use a crane or something similar? Storage space for material is also missing. Do you want to lay the compressed air lines throughout the entire house? You wrote the compressor possibly on the attic.