Thanks for the response.
I think I understand that germinating a seed does not require anything more than an inert medium, like coco coir. You mentioned that would be good enough for the first few weeks.
Do you transplant the seedlings into a potting mix after the first few weeks if you need to continue to grow them out for 8-10 weeks?
In my case, I am planning to start tomato and pepper seeds in 3-inch net pots and hope to keep them in that net pot for about 8 weeks. In order to do that, I think I would need something more than an inert medium, like coco coir, because the growing plant would have to be feed by the medium after those first few weeks. Therefore, I bought the potting mix which I hope will both start and feed the plant for 8-10 weeks until it gets transplanted outside. Am I on the right track?
In the past, I just purchased 6 packs of vegetables at the nursery and transplanted them directly into the garden. This is my first year of attempting to start seeds in house, grow them out for 8-10 weeks, and then transplant them into the garden.
Frankly, I did not consider that the type of seed starting and growing medium for in house early planting needed to be any different than sowing seeds directly into the garden. But the more I learn about early seed starting, the more I am finding information about garden soil and/or compost might be disadvantageous for seed starting in house.

If I totally muck up the early seed starting and growing in house for the 8-10 weeks, my backup plan is to just buy more 6 packs of vegetables for direct planting after our last frost date. However, I have a few specialty seeds that I know our local nursery does not grow out, so I really hope they will sprout and grow out in house.