Wow I cannot imagine an acre of onion seedlings. I sow mine in a window box, sprinkle soil over top and water down and it goes under my light. I can't get Candy Onion Sets around here and they are expensive to buy and have shipped (I have done it from Dixondale but realized much cheaper to do it myself). Good to know about trimming them down, mine on my shelving unit are all up in the lights and no more room to raise the light. They are small when I set them out - some were no bigger than a cofffee stir stick - but in fall I have nice HUGE round candy onions that I pull, cure and they keep way up into the winter before I use them all up. I am also growing some spanish onions too. They were pretty easy to start and just look like little blades of grass coming up. I just let them grow, stick out in the green house usually sometimes in March or April and then plant out.