I wintered about a dozen 4 frame medium nucs in homemade polystyrene boxes last winter. It’s possible to get them through winter as a small nuc. However if you have brood to spare, bigger always better when it comes to bees and winter.
Due to moisture issues, I would be hesitant to stack nucs on top of nucs. Good insulation is a better way to conserve heat IMO. If you want to get into extreme pampering, there is always electric heat