KSB are pretty voracious because they are a smaller species mice are ideal, even as adults while they can take rats fuzzies/pups, mice are a better choice the equivalent size in mice means a leaner prey with bones fully formed which you do not have with rat fuzzies/pup, so in the long run your KSB will benefit from that.
When young and feeding on pinkies feeding every every 3 to 5 days will be important considering the prey size is meaningless and does not offer much nutrients (it's basically a blob of fat and water)
As they start to eat fuzzies you can do every 5 days and than once a week when you get to bigger fuzzies/small hoppers.
Now as far as how to feed them simply move the f/t feeder right over the top of the substrate and watch a remake of tremors happening right in front of you.
If you feed live simply drop the feeder in the enclosure.