Don't despair, you'll get better at it.
You were right about the light....you are trying to copy nature, so 24 hours of light is too much. Plants need to rest too.
When grown from seed, plants need to be “hardened off”, just as you described. Outside for an hour or two in the shade the first day or two, then two to six hours for a few days, then 4 hours in a mix of sun/shade, for three to four days. And don't listen to me about the timing, watch the plants. If it's too windy you won't leave them out for as long, as they will dry out fast, and possibly stress themselves.
The idea is to allow the plant to ‘learn’ how to deal with changing weather and wind slowly.
It sounds like you're doing OK with the peppers and tomatoes. Good.
Any plants you have growing in a sunny window need to be rotated every day. 180 degrees.
The best part about starting from seed, is that if you want 6 plants, it doesn't cost much to start 18 seeds, and then only plant the strongest survivors.
Always remember...
The plants want to live even more than you want them to. IOW, they are going to try to live regardless of what you do. So keep trying.
I use (mostly) newspaper pots; 3 seeds to the pot. When up & starting to form true leaves, pick the weakest & snip--DON'T pull!--at soil level.
A few days later, repeat, keeping the strongest & ending up with 6 pots with one good seedling each.
Saves on space and pots, though if using peat pellets or such, there isn't enough room to space the seeds far enough away from each other.
In one of the books I reccomended (Dick Raymond's book) He talks about how plants are like people. They all need food, water and sleep. Some like hot, some cold. Some dry, some wet. Some crouded, some solitary. And like people you have to figure them out and the best well to get along with them.
Thank you all for the tips. I’m going to keep trying on the seedlings. I’m hoping to direct sow more seeds this weekend. If those survive I may never start them indoors again! :0)