The OP brings about €100k in land
so what? then you can easily keep sleeping on your converted Billy shelves
Regarding the whole 0% financing discussion, I abstain. To me, it is and remains a marketing gimmick. You end up paying somewhere, even if it’s the missing discount. In the end, you are so restricted by the providers because you depend on their 0% that you get annoyed.
Here’s a last tip. If you take out the additional €20k construction loan and don’t spend it on furniture, just make a first special repayment.