If he is the only duckling you have hatching out, wait until he is dry and fluffy then you can remove him. If there are other eggs that should hatch, wait for all of the eggs to hatch, or three days from the first hatch if no other signs of hatching or visible, then remove all ducklings/chicks.
Yep that is normal. It will take him a while to regain his strength after hatching. It takes a lot out of them. Once he has his strength back he'll roam around the incubator and may move the other eggs a bit, but don't worry. It won't hurt the other ducklings. Let your other two ducklings hatch and dry, then you can remove them all.