Are you asking me, and if so did you mean 1000+ instead of 100+???

I use whatever I use - when I get tired of raising seedlings, think it's too late for more seedlings, or whatever, I either give the rest away or "save them for next year" -- which generally means I find them on a shelf two years later and throw them away.

I tend to balance things out a bit--bulbs for early spring. Copious aconite and crocus for a late winter show, a succession of tulips for very early spring to late spring, several daffodil types for mid to late spring, and a variety of oddballs (snow glory, hyacinth, and plenty of others) for launch throughout the early season.

May marks the end of the bulbs. At that point, the annuals pick up and I use ones that bloom all season long for the most part, and that takes me to first frost in late October. The chrysanthemum, fall crocus, and aster pick up then. By that point it's November and the garden more or less shuts down except for the remaining evergreens and snapdragons (which stay up into January, usually).

Already started. The Lisianthus are under light and a seed warming pad, but haven't sprouted yet on day 11. That's not unusual.

The Cleome are next and get brought in as soon as the Lizzies are up and ready to go under full light downstairs--probably a week or two yet. Petunias go about the same time, with the salvia also starting in February once the petunias are up.

It does depend on your space and what you're doing.

For marigold and zinnia, six weeks is more than enough, and they'll get huge. I like to give my petunia more time, and I trim them to divide the central stems into more, so I start those in February--but March is OK.

Cleome and Lisianthus start early because they need the time. Both are slow to grow and develop, and you want them to bloom in a reasonable time frame in summer.

I like my salvia larger than average, so I start those early as well--late February. It also speeds the blooming when planted.

The Teddy Bear Sunflower get staggered because they only bloom three times. They'll range from February to April.

However, my shelves are tall, the lights are adjustable, and I can deal with larger plants.

It depends:

Marigold, zinnia, salvia: 72 cell trays. You water a lot, but the plants can deal with it and don't mind being rootbound in their cells. Most plants do fine in 72 cell trays.

Cleome, Melampodium: 60 cell trays. I could use 72, but both tend to do a bit better with a touch more space. I'd also put verbena in these.

Wave petunia, sunflower, Lisianthus, other things that dislike being transplanted or get very large: Solo cups, or the generics from the grocery store. Very few species require these, and you can usually tell by how large the plant is when mature or if it specifically says it doesn't transplant well.

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I'm not sure where you're looking, but I like these guys for basic greenhouse kits. You'll only use the plastic top until they sprout (but you do need it until then), and the bases are reusable. Last year I only had to order the cells.

You'll be fine with larger cells on those, but growth will probably stall in April sometime. That's no big deal, it'll resume once they're planted. When planting, you're going to have to open the root binding on the plant to let the roots free, but that's just a matter of teasing things apart a little bit (and a good idea with any root bound annual you're planting).

Yeah, that's a bit small and a bit low powered. I use 4 four foot forty watt T12 bulbs per shelf (less efficient than the T5 bulbs, but cooler so plants touching them doesn't matter at all, plus easy to source). Two are warm white, two cool white to try to balance the spectrum a little bit.

Home Depot has a basic work lamp for $10 or less (in a small but long red and white cardboard box). The ballast won't strike under sixty degrees, but since my cellar never goes under 62 that's not a problem.