Hey, thanks for your answers.
The only pre-existing walls are the exterior walls, and these are brick - almost 100 years old. Some inner walls between bedroom + closet and remaining space, nothing more.
As far as layout, this is a ~900sqft, with one large open space (incl kitchen, dining, living, hallway), one bathroom, and one bedroom. Hope this helps.
I inquired my contractor about heat conductivity and he says he will have additional layers on top of the steel studs, making heat conduction a non-issue.