To keep things simple, I had originally decided not to start seeds indoors to create transplants. But this idea for onions, available on the Savvy Gardening blog - https://savvygardening.com/why-planting-onion-seed... - caught my eye. The blog post describes a method to start onion seeds in plastic containers outdoors in winter, and the transplants can be placed in the garden in spring.
Following the instructions, I created the seed container in January. Unfortunately in late March, it tipped over in a bad storm so I had to reconstruct it. Add that to the fact that I couldn't plant anything in the raised beds until early June (my cover crop mishap), and I was doubtful of a successful outcome since I was supposed to plant the onion transplants into the beds in early spring. But in early June, I went ahead and planted the small shoots from the container. As of today, it seems to be working!
The tops have grown substantially, and last week I noticed the bulbs starting to protrude at ground level. Was this normal or did I not plant them deep enough? It seems that this is normal. It's time to harvest - then cure - when more than half of the tops have fallen over and turned yellow. Not there yet, but I'm optimistic.