Last year was my first attempt at onions from seed but they didn't work out. I started them inside way too late and plated them in the garden when they were too small. Our soil was too dense and the area they were in got muddy and they rotted early in the season. This year we are getting a soil test done and will add amendments to hopefully lighten the soil a bit and help with the water retention issue. I've got my seed starting stuff ready to go and want to give onions another try. I have Walla Walla onion seeds. With most of my veggies I typically start them in seed starting trays (cells) and then transplant into plastic cups when they start to outgrow their cells. By the time they are outgrowing the cups it's time to go into the garden. With onions being root vegetables I wasn't sure if they'd deal well with being transplanted twice-once to the cups and once to the garden. What do you all think? Am I better off planting them in a larger container from the start?
I also have a question about lighting for them. I know onions use length of daylight to determine when to bulb. I will be using long day onions. With all of my other seedlings I typically turn my grow lights on when I wake up and off when I go to bed which means they get about 16 hours of light. I need to avoid this with the onion seedlings though, right? If they get that much light they'll bulb prematurely. I read they should only get about 10 hours of light as seedlings. Can the rest of my plants (tomatoes, eggplant, peppers, herbs, etc. which will be started in a few weeks) do well with such little light or should I put the onions under their own lights?