Onions will let you know when it is time to harvest because the green stem will flop over. Since the bulb forms above ground, it is easy to pull them.
As for curing, I put them outside in a single layer out of the direct sun under a roof so they don’t get wet. I have a gazebo which has tinted corrugated polycarbonate sheets in the roof that filters the light just right. Also, I put the onions on a rack so they get good air circulation.
It is time to bring the onions in sometime around two weeks. When the onion is cured, it will have a papery skin on the outside and the green neck will wither and brown. Once they are cured, I trim the neck about an inch above the onion and trim the roots. I gently brush off the excess dirt.
After harvesting and curing, do NOT get the onions wet or they won’t store well.
I am storing them on a moveable rack in the basement where it is cool and dark. When I stack them, I put a piece of burlap in between. When winter sets in and our heater turns on, I will have to move them to the garage.