I cover mine with plastic kitchen wrap until the first shoots appear. Never had a problem. For extra fast germination in my (cooler) basement, I place the kit on top of a warming mat.
If you are carefull with the cells, you might get 2-3 seasons.
The actual trays are 10" x 21" and the individual planting containers are 3" deep and 3.5x3.5. For me they were the perfect size for what I was planting; perennial and annual flowers seeds. As for the volume for overall tray, I didn't keep track but what I did learn was that you should fill the container to the top before putting seeds in soil. The soil packs down over time due to watering and until the seedlings are a few inches high, you can not add soil or you will suffocate the seedlings. There are 18 containers in each flat. I would suggest separating them at the beginning. As the seeds take root, some mature faster then others and you may want to move then around....closer to growing lights, closer to natural light, cover some and not uncover some when they sprout. If you separate them in the beginning, it makes it easier to move the containers around later. It's pretty easy. Just take a sharp utility knife and it will do the job. I did also purchase the containers that are made of a cardboard material and I do like the square ones much more. Just my preference. Besides they fit better on my 3 x 8 planting tables being squares then the round ones.
It depends on the density of the soul. There are some spoils that are more dense than others. I would ask the pros at the garden center at Home Depot on which soil to use. I did read somewhere to not use old soil. But what I did learn was to fill them all the way to the top with soil. Most seeds take 7 -21 days to sprout and by then, they soil has packed down due to watering. That is only natural. Now I am a bit worried that in the end I may have to transplant some because they may not have enough room for the roots to grow and you don't want them to become root bound before you get them replanted.
I find it cheaper to fill with potting mix from a bag. I like the organic mix sold by HD.
The pots have small slots on the bottom so they can draw water. The tray is solid so you can pour water either on the dirt or in the tray so the plant can draw water from the base.
we don't offer in stores individual Pots to replace