I don't know if there is an formula answer to the questions. I do know in spring, with young bees in the hive and a flow happening there really is no limit to what you can transfer from hive to hive.
In spring I will gather brood frames with bees from a bunch of hives, mix them together in transfer boxes and then distribute them to hives I want to boost with no problems.
If a flow is on, I would transfer a couple of frames, put them beside the brood nest of the nuc, possibly leave a empty frame between the brood nest and the new frames. Without a flow this should still work but the risk is a little greater.