Windows from Poland or Bosnia?

Yes, that rings a bell, and I would consider it recommendable. Several good white label manufacturers are located in Benelux.

Then it fits perfectly. The windows will be ordered tomorrow: powder-coated, with concealed fittings and Purenit sills on all floor-to-ceiling windows, warm window sills, Ug 0.5, pre-assembled upper boxes, and venetian blinds. Did I forget anything important?
I hope I won’t regret it ;)