I use a lot of onions in my cooking and meal preparation so plant a big bunch of them each year. (No, it's still a wee bit quite a bit early to put them in for this season, but it's coming.)
I plant both red (Red Comred) and yellow (Stuttgarter Reisen) onions and normally use about the same amount of each variety. A total of three 4' x 8' raised beds are devoted to growing them every year. I plant them fairly close to each other, about 8" apart in each direction, which works for me.
Keeping our onions over the winter months hasn't been much of a problem as our basement that stays close to a constant 52° seems to be a place where they're happy.
Curiously, last year the red ones developed much larger than the yellow ones so I knew there should be more of them left this spring. I've been noticing some of both varieties were starting to go . . . sprouting big green shoots or developing mushy/rotten spots . . . so it was high time to sort through all the remaining ones.
Brought them up from the basement and spread them on a table on the deck. Gosh, I had more than I thought in those two crates.