This needs careful attention
The management of a nucleus needs careful attention, especially in the couple of weeks or so after it is made up. At the point of being made up their condition can vary considerably. If it has come from outside flying range, it may be fairly well balanced with its own force of flying bees. If it is put in the position of an existing nuc, it will also have a flying force, but if it is made up and placed in the same apiary in a new position it might have no flying bees. All these situations need different management, so obviously I can only give general advice here. A nuc or colony that is denuded of flying bees, will push forward younger bees to become foragers, so in a few days will be flying as if nothing has happened.
I am assuming we are dealing with a nuc of 5 B.S. frames or less, possibly down to two. Whatever the size, I would allow for the equivalent of at least one full frame of stores most of the time. That should last most nucs for a couple of weeks, even if no food came in. I don't like feeding bees during the summer, unless absolutely necessary, but in my view it is bad beekeeping to allow colonies to get very short of food. Poor nutrition exposes a colony to major problems. In most of my colonies there are usually frames of food that can be used, or where I have brood combs drawn out above queen excluders, there are usually frames of food I can use.
I will only deal here with the management of nucs that will be used for increase, not any of the many other options. I assume that a queen or queen cell has been given. A check to see that the queen is laying is important, especially so if a queen cell has been used, to make sure you have a good viable queen, and that she is not a drone layer.
You must remember that a frame of brood becomes 3 frames of bees when it emerges, so if you made up, say, a 5 comb nuc with 2-3 frames of largely sealed brood and put it in a 5 frame box, then you must expect it to explode in a short time. Don't ever think a nuc can't swarm!.
A nuc will expand much quicker if it is given frames of comb, rather than foundation. I don't like using foundation in brood boxes. If there is a nectar flow on, the bees tend to extend existing cells with stores in, rather than draw the foundation, making very uneven combs. If there is no income they climb all over the foundation, then chew holes in it.
It is a mistake to have the adult population so low they have trouble covering and tending the brood, as this just hinders the progress of the colony. I like to see nucs with frames well covered with bees, to the point where you have to move them to see the brood. This allows you to place an empty comb either on the edge of the brood, which I usually prefer, or in the middle, which I avoid if possible, because I don't normally like splitting brood up, although there are usually less problems with comb than foundation, because the queen can usually lay in the comb within a day or so, yet the foundation has to be drawn first.
I tend to "work" my bees a lot harder than most beekeepers do. I often move frames around, perhaps to weaken or strengthen colonies. A small nuc, if the frames are well covered with bees, will expand quickly if given a comb of sealed brood, minus bees, then another one 7-10 days later. A colony can be rapidly built up in this way.
It is crucial that an expanding colony isn't cramped for space, so look at the amount of brood and its age. Learn to assess what will happen in, say, 7, 10 or 14 days time, but this is down to observation. Very often a 5 comb nuc with 4 frames of brood will fill a full brood box in 7-10 days. If you think a bigger box might be needed, it will be!
Even though you may not have set the nuc up in the best way for the bees, they will soon put it right if they have enough bees to do it. A brood nest is normally circular or oval, with more brood on the combs towards the centre. Combs towards the outside may have less brood on the outside of the comb than the inside. Pollen will be above and around the brood, with liquid food outside that. To help expansion you may be able to turn round the outside combs, or put them in the middle of the nest. This will allow the bees to remove the stores that are preventing them from having a circular nest, so they get the queen to lay in the vacated cells. Don't stretch a colony further than it is able to comfortably look after the brood.
The smaller the colony, the more critical the food situation can become. This often depends on the stage of the brood. Young larvae are incredibly hungry, but sealed brood doesn't need feeding. In a week during a strong nectar flow a small nuc can pack the box out with food, yet in a nectar dearth it can use up a reasonable amount of food and be on the point of starvation.
I usually have a lot of nucs of varying strengths during the summer. They are very valuable, but need a bit more care than full colonies. A bit of understanding and thought will make things much easier for you and the bees. I put nucs in the shade to give them the best chance of ventilating the box. I always use small entrances in my nuc boxes to avoid or reduce any possibility of robbing. Although I use polynucs, I prefer my own design of wooden nuc box. The standard ones have solid floors, but I have some without floors, so I can have as many boxes tiered as I like. This is useful for build - up or uniting.
These are just a few ideas for managing nuclei. In my experience you can probably learn more by observing a nuc, than you can from a full colony. Bees are very adaptable and will deal with most things beekeepers chuck at them. If you have an idea, think it through, modify it if you want to, then do it. If it doesn't work, find out why and learn from it.