Hello
I grew Senshyu (Suttons) and HiKeeper (T&M) from seeds last year. Starting them off in a seed tray in August then planting out October time.
None of the Hi Keeper plants survived the winter and I lost about half the Senshyu - but the survivors all went on to produce a good sized onion.
They seem to need to survive the winter as tiny plants and don't start to make a bulb until March. Then you feed them with copious amounts of tomato food and away they go.
On some of the packs it suggests you sow them in the ground like spring onion seeds then thin them out in the spring and that may be the way to go if we have another tough winter and you thin the survivors to a complete row.
But the nursey bed thing is fine too.
Good luck, i will give them another go this year and you get a lot fewer of them bolting if grown from seed, definitely.