So, my sister-in-law is currently building in the greater Munich area. 160sqm with a basement and double garage costs them 700k. But additional construction costs of 50k, kitchen 20k, terrace, house entrance, driveway 20k+, furniture, photovoltaic system 15k are still missing. So at least 800k. You are planning an even bigger house at a later date. Therefore, I don’t think 700k for a turnkey house is possible.
Otherwise, everything sounds good with you. I would just leave out the basement or build it smaller, then it should be more relaxed. But you can get quotes first, then we’ll see.