I recommend that you plant both onion sets and seed. If you have a seed planting problem, you will not be without scallions. I found Crimson Forest to be quite tasty. You will have to try several to find the one/s you like best.
Here I plant seed outside Oct 1, and transplant Nov 15. Onions are usable just as soon as they are big enough for you.
You will likely have to plant seed under lights about 6-8 weeks prior to transplanting outside. (my transplants are just about big enough to pull for green onions now.)

In our zone you are better to start from seeds inside about 10-12 weeks before you intend to transplant. Every 3-4 weeks after they germinate give them a haircut to 2" so they will grow more stocky with larger diameter stems for transplanting. For bunching onions I omit the plastic mulch since you usually have most of them harvested within 8-10 weeks after transplanting. I typically plant at 4" intervals as shown on extreme right row of picture.

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bmoser I assume the onions under the plastic are going to have large bulbes. Will the bulbes be under the plastic and if they are how dose that work for you? I have always wanted to try planting onions that way but never have. I'am very interested in how works for you. TIA YOPPER

yopper, I guess I responded to your email. i'd like to add that an mature onion formed under the plastic can be easily missed. I remember seeing just the shriveled stem on one protruding above the plastic which led me to reach under and recover a huge 4-5" onion. I immediately started feeling in all the suspect holes on hands and knees pulling up almost a bushel til I was finished.

Your onions look great. But the black plastic with drip tape (2 lines) is of real benefit for warming the soil and providing a constant water supply. Those are mandatory provisions if you want to sell as "PA Simply Sweet".