Today, I finally got to harvest the onions. They are smaller than I'd hoped for, but once the tops start to die back, it's time to harvest. I should've taken a picture of what they looked like before I pulled them up, but, basically, they just looked like a strong wind had blown them over, and they were beginning to brown.
You know what they say about hindsight, right? Well, according to my reading this morning, my bulbs may have been bigger if I'd laid off the fertilizer for the past 7 weeks or so and reduced the amount of water.
The onions that bloomed are mostly still standing and seem to have bigger bulbs under the soil. I will give them a few more weeks to show signs of dying back. If they don't, though, it'll be time to harvest, and we'll have to eat those bulbs first as they likely won't keep as well as the ones that die back on their own.
To prepare the onions to last awhile, I cleaned them up and laid them out on the porch (any warm location will do). They'll stay there for 2 weeks (unless they're all eaten up by then) and will then be ready for cooler storage.