My ducklings LOVED peas. Which I believe has a decent amount of niacin in them. I would roll the peas on the floor and let them run after them. Also, they loved to eat peas out of my and my kids hands.
Realistically, you want 1 drake per 3 or 4 hens. Honestly, the more hens the better. I learned my lesson by having one male and one female, because I believe our drake over mated my hen and she passed in January.