Since I've mildly been using gardening to pull me out of a dissasociative episode, I don't have as well documented a timeline of my broccoli plants as I would like but here's what we've got so far.
I sprouted the broccoli seeds in an old egg carton. This is the earliest photo of their development. I probably planted about 6-8 seeds per cup in the egg carton. During this process I kept the egg carton in a window that recieved a lot of sun. I used a spray bottle from the dollar store filled with water and sprayed the seeds every morning to keep the soil moist.
When the seedlings get to be about this big you'll want to thin out all but one seedling per section of egg carton. The leaves visible in this photo are seed leaves (the first two leaves that sprout out of the initial seed). Do not pull the plants you are thinning out of the dirt. Instead use small scissors (embroidery scissors are a good size) and cut all of the smallest sprouts at the base of the stem. This will help to protect the remaining Broccoli sprouts fragile root system.
The two leaves on each broccoli sprout are seed leaves. These are not what the rest of the broccolli leaves will look like. True broccoli leaves (shown below) will emerge shortly after the seed leaves. Once a broccoli start has two true leaves it should be moved to a larger pot. When transplanting remember that broccoli plants have fragile roots and the egg carton is bio degradable. You do not need to remove all of the egg carton and should leave any amount of the carton the roots may have grown through.
All of the research I did suggested transplanting starts to a larger pot for a while before transplanting directly outside. I transplanted two plants into small pots and one directly into a raised garden bed. I wasn't able to get photos of the transplant process but I ended up keeping 3-4 total plants at this point.
To learn more HTML/CSS, check out these tutorials!