Underfloor heating in the children's room? Some rooms planned without underfloor heating? Air-to-water heat pump removed?

You create more problems for yourself with such special solutions than you want to have. Interior insulation is especially tricky.

I would try to keep the house construction as simple as possible. There will be enough points where it creaks anyway.

You can be exempted from the [ERR], but yes, this depends on the technical understanding of the caseworker.