A radiator system isn't very efficient, esp. if the radiators are covered with something (marble?).
The first thing that should be done is to get a REAL architect or civil engeneer to figure out the heat demand of the building.There are three major figures: the total demand per year expressed in "kWh/a" and then the max. demand expressed in "kWh/m2max" and then the normal load expressed in "kWh/m2".
For the decision if it's worth to think about a heating system/any heating system the last number is the most important.
To keep this number at a low value it is most important that the house is designed not to loose energy.That means a good insulation but also a good design. The design is the first step: make it compact. No baywindows or other things sticking out, no pebble dash.
Then keep it hole free, no chimneys, no pipes sticking through the walls.
Then make it draft free, no holes(again!), no exit doors eqipped with letter boxes.
Insulate ALL fabric parts, incl. the ground floor, from the outside. Forget the usuall double wall system, insulation belongs on the outside. Insulation is there to protect the building, not to be protected by the building.
And then check the previous posts about home heating here on AAM.
A ZERO energy house can be constructed for as little as 5% extra of building costs. Tell your engineer that this would be his job. And let her/him sign a guarantee on this issue.
If you can't find a competent engineer check the web for "zero energy homes" or a similar search word, there is plenty of competition out there.