Feeding more that one US gallon (3.5 liters) is not necessary. One feeding to get them started on the comb and then let them go (I often don't feed swarms at all). Super at the same rule of thumb you use for the rest of your apiary.
There are different styles. Does swarm nees syrup, ofcourse not, but I do not like that they use valuable honey 16 lbs to draw up combs. My style is feed swarms
It hive gets a lot nectar outside, it is not wise to give sugar at all.
But if they do not get nectar from field, I give 20% sugar syrup untill they have drawn almost all comb. When they use 20% solution, they use almost all. If you give strong syrup, they store it in combs and cap it.
There is no difference with package bees and swarms. Why to feed packages whole summer and swarms not at all? Both need combs.