What loan amount is realistic for house construction?

Little equity, little income, costs calculated ultra tight: you are running towards disaster.

Just wait another 3-5 years. Income will increase and everything will become more relaxed.

The girlfriend's income should definitely be increased as well. There is still a lot of room before maintenance obligations apply, and even beyond that, 50% is only due after various deductions. At the latest when children arrive, the income will be significantly reduced again with a half position. Speaking of children... how do you plan to cope with the financial losses?

Paint once or twice? How are the ceilings treated (plastered, primed, wallpapered, painted)?

Floor materials, i.e. adhesive/impact sound insulation/cut-offs/baseboards/acrylic also have to be paid for.
Oh yes, walls in the bathrooms? Just white as well, or are tiles going somewhere too? Stainless steel edges also cost a lot of money. Etc.

You are still approaching this very generally and naively.

We are almost finished renovating ... don’t worry - no one is naive. For acrylic and other "building materials" you should anyway plan another €10,000 as an extra item. I would also calculate tiling work separately. The same goes for the ceilings – depending on whether they are simply plastered and painted or need to be suspended, etc. Very generally speaking, for simple walls and floors the 10k fits. Tiles, suspended ceilings, etc. should be calculated and also accounted for differently.

We are almost done remodeling... don’t worry - no one is naive. For acrylic and other "building materials" you should anyway plan another €10,000 as an extra item. I would also calculate tiling work separately. The same applies to the ceilings - depending on whether they just need to be plastered and painted, or if they need to be suspended, etc. Generally speaking, €10k is about right for simple walls and floors. Tiles, suspended ceilings, etc. should be calculated differently and also accounted for separately.

I just wanted to point out that the OP has rather underestimated and calculated too low!

We have 2 plots in close selection, one about 900sqm/70k euros (incl. tax, notary, land register entry) and the other 1000sqm/100k euros (incl. everything - fantastic location) - location Bavaria towards a small town.

Is there a catch? I thought Bavaria was that expensive.

Is there a catch? I thought Bavaria was so expensive.

Maybe Lower Bavaria or outskirts? Around here in Upper Bavaria, such plots would cost four times as much.

Same here. It may still exist in very rural areas.