I personally take them out when they start to meander, as they knock the other eggs around. (this isn't a problem in a nest environment) I just grab quick, and off to the new digs, where food, padding, etc and waiting. They dont' HAVE to eat for the first 24-72 hours, but I feed mine and...
Ducklings can be unstable. Id put non slip mat under him (like the kind for cabinets - it washes easily) its soft and good for his feet. It will only take him a day (or less) usually to have their feet under them properly.
The temps are good. Help him get his first drink of water, and then...
Glad Iain was around to advise you. I agree, duck looks like its gonna hatch OK. Your humidiy will probobly be ok, but I up mine further by washing/bleaching/rinsing and then adding a new sponge thats soaking wet leaned against the side. It really helps in tough humidity situations.
Good luck!