Your best place to start is by reviewing the FAQs over on the Growing from Seed forum here. They cover all the basics on potting mixes, containers, watering, lights, feeding, etc. Don't know how indoors could be too cool but better cool than too warm as it bolts when too warm.. But like any houseplant it will need good lighting. You might also check in with the folks over on the Herbs forum for any special tips they may have, Dave Here is a link that might be useful: FAQs: Growing from Seed

Not likely given the high day/night temps May-Sept. You are already off to a great start going hydroponic though. I had 20 acres in Indian River County and only planted in the ground one season. The sugar sand just dissolved any organics/fertilizer that was applied. It was much more efficient growing in plastic half barrels 3 plants per pot with good trellising. Never used fungicide and the biggest pest problem was leaf footed bugs which would eat the maters late in the season and cause me wilt problems. Still 30 plants in barrels yielded better than 238 in the field! Your best bet is to start your seeds around August 15 or so and get the plants set out Sept. 15-30. Depending on your part of Florida, this would give you good yield until you would need to be concerned with frost. A good trellis system allows you to cover your crop should cold weather arrive. Then a second crop can be started in January that should carry you through til mid to late May, when the plants will just start to stress from the rain, heat & humidity. If your plants are still healthy/disease free when cold arrives you could also start cuttings. I still do this in TN for a later fall crop. Sorry for the long answer, hope it helps.

There are quite a few different hardiness levels in all the onions, including the multipliers. See Heirloomonions.com. There seem to be quite a few heirloom type multipliers from across the south, with different names for them depending in part on where they come from. Here in Minnesota I have had good luck with both fall and spring planting of my yellow mulitpliers that I got from Jungs, some years ago. I have not had good enough multiplication on Kelly's to risk any fall planted yet. For me they are not as prolific as the smaller yellows, although significantly larger. IMO they don't keep quite as well and also take a bit longer to mature. Next fall I intend to cut back my garlics to a few faithful varieties and fall plant my yellow multipliers again, and if I get a decent enough return on the green mountains I have, I will fall plant some of those, too. I just put out my spring onion bulbs and sets yesterday and am still waiting on plants from dixondale. I do believe I shall have more than enough for daily consumption AND planting back plus quite a surplus, since I am by myself. We are quite a bit behind you, even if we are ahead of normal this year. In the past this would be about when the frost goes out of the ground, but this year that happened well over a month ago - not just early but way early!

i live near the gulf coast, south of houston, i garden in raised beds, we have a lot of humidity, drought then torrential downpours and high temps 10 months out of the year plus it's frequently very windy....our soil is gumbo (dense clay) anyway my best herbs are thyme, the oreganos are probably the best and parsley in cooler weather (before it's 90 degrees practically around the clock) rosemary does great too and has lived for years for me, fennel will thrive for a couple of years... sage, bay tree, chives and basil (in the hot months) i also have a three year old dill, planted in dappled shade-i thought it was dead, but it came back drainage is the key to raising herbs, mine grow in rose soil over raised bed materials i've never been successful with growing them in pots, except for oregano and mint.... i have also kept lavender for a few months at a time, never for the entire year so loose, well draining soil, don't water them on a regular basis and just let them go..... as long as roots are don't stay too wet, they should all be ok and they love our cooler months