I understand that nuc is volume of 5 frames or? Then you give foundation frames and bees start to build and make brood? Is that so?
When you want to get your hive rise, feeding is not essential. I have same situation when I have 1 kg little swarm.
1) Most essential for little nuc is warm of hive. There cannot be extra space. If they have, development will be slow.
2) Insulated hive would be really good and extra wall in the middle of Langstroth box.
3) In the hive it should be one frame food and others brood. If they have more food, it is bad thing.
4) If you feed over, it limits brood area and slow down development
5) Colony is at it's smallest 3 weeks after installing. Half of buyed bees have died.
6) When 3 frames full of brood have hatched, you have a full box of bees or more.
Now you have summer. There is not reason to feed bees . They get from nature food what they need and they build more space if they can.
The number of bees limits the development of colony. You cannot speed them upp by feeding sugar. It just stuck the free space of hive.
If I have a little colony, which have 2 or 3 frames, I take away filled frames.
If you heat with terrarium heater that tiny colony, it can make 100% more brood. 8 W in your climate is enough.
If you should use insulated box and limited space, it speed upp development a lot, 30% I suppose.