@Dwf1942 -- I'm a little late to your thread, but I grow lots of onions in my garden, and am in a more or less similar zone, so here are my recommendations:
Grow from seed or plants, not sets, to get nice big onions.
The really sweet onions, like Vidalia, Walla Walla, or white sweet Spanish, do not store well; so, buy them or grow them, and use them up quickly.
"Candy" is one of my favorite varieties -- it's "day neutral" and will grow in pretty much all areas of the country; otherwise, look for "long-day" types (Johnny's Selected Seeds has great info about where the different varieties will do well).
To get large onions, they need room to grow; so either space them out (around 6" apart) at planting time, or plan to thin them by using some as green onions.
I agree with ZenMan that this is about the time to start your seeds; I start mine around Feb. 15th, in 6-packs in flats, under fluorescent lights. I plant 5-6 seeds per cell, when the plants get about 6" tall I trim them back to about 4" (you'll have to do this 2 or 3 times), and then around the middle of April I take the plants out of the cells and move them to 3" pots with about 15 plants/pot. Then trim them back as needed, because when they get too tall they are a real mess. (you can use the trimmings like you would chives)
Onions should be grown in full sun, and, because they are so shallow rooted, you want to keep them weeded (and watered) so they don't have a lot of competition for water and nutrients. And they're ready to harvest whan about half of the tops have bent over (although I usually wait longer than that, until the tops have pretty much all died down). As Sally said, spread your onions out on screens or something, so they can dry well; then cut the tops and roots off, remove the loose skins, and store in mesh bags. (or, actually, I have had very good luck storing them in paper grocery sacks)
Happy gardening! I hope you have good luck with your onions, they are one of my favorite crops
