I spent several years in Vidalia. ALL of the 13 counties that make up Vidalia plant from sets. I grew mine from sets. I highly recommend you not bother with seeds - it is not worth it. I think all the Vidalia's are Texas Sweets. It is the soil (low sulfur) that makes them sweet.
I used to see dump truck loads of onions go to cow feed simply because they were too large or had two onions growing in the same bulb.
My specialty was designing the hardware and User Interface (Visual basic) that controlled the drying or curing of the onions.
I sat down with the nations largest onion producer at the time - Bland Farms, and spoke with the owner, Delbert Bland. He told me him and his Dad had a bet going that he (Delbert) could not grow a hundred thousand dollars worth of onions on a single acre. Now, being into seriously obnoxious agriculture - I was all ears. He grew these beautiful "Green Onions" that were about 16" tall and sold them to Publix. He won the bet and showed me his new truck that was the bet.
I was amazed to see that much money come from such a small place and be legal!
I was extremely amazed at the ignorance of the Farmers at that time. They had little concept of how to treat the product after it came in from the field. It was really sad - but they learned. Most Farmer do not consider post-harvest - they just think "inputs". When the whole crops rots - they cry and learn. I will tell you from unfortunate experience that it is very sad to watch a Farmer cry - it has happened several times.
I visited a potato Farmer once a long time ago (I used to do potatoes). It was a social call, nice guy. He lost a thousand acres of potatoes. He was sitting at his desk - next to his safe bawling his eyes out. I left. He died after that. He told me that that part of the state of Florida would never have a privately held farm of his size after he died. Estate taxes had to be paid and the land had to be divided.
I dealt with another Farmer recently. I think he was one of the bigger Farmers in Florida. His farms were SOOOOOOOOOOO big, they each had their own runways and were registered with the FAA. You could easily see their farms from space. Rumor has it the farms sold to Bill Gates?! I had heard the super rich were buying farms - maybe so?