I can't help much with success rates. I'm not that scientific or particular. I grab seeds, sprinkle them in a jug, and move on. I never count seeds or figure the % that sprouted. But I am rarely disappointed; I usually end up with more plants than I can handle and end up giving a lot away to friends. I know that some people do track percentage but I never have. Seems a waste of time for me.
I have to admit I'm not too particular about planting depth, either. If you google "seed planting depth" or something similar you'll find some recommendations. Trudi addresses this in her site, too.
http://www.wintersown.org/wseo...
Some sites say that if seeds need light to germinate they should be surface sown, those that need darkness should be sown deeper. Trudi has an answer to that, too. "For every day, there is also a night".
I assume you intend to cover the pots you sow in during summer? (Covering increases humidity which increases germination). If so, I'd give 'em lots of vents and keep in dappled shade. In your climate they might cook in sun. Seems in might be easier and even work better in winter to avoid the heat stress in Texas. But I probably shouldn't guess about your climate because I garden in Ohio. (Feels like Texas now, 90° with heat index 99)
And there's a thread on the wintersowing forum about summer sowing
http://cubits.org/Germination/...
There is a thread in the seed cubit about potting mixes
http://cubits.org/Germination/...
I prefer a quality potting mix. I don't like germinating soils because I find them too fine and I think they compress too easily. Some of my favorite brands are Promix, Fafard, and MetroMix. Most wintersowers I know use Miracle Grow. I use potting mix (not seed starting mix) for everything. Everyone has their favorites, though. I also usually sprinkle fine grade horticultural vermiculite over the surface. Why don't you want to sow the seeds in winter?
If you click around the seed cubit I think you'll find a lot of the info you're looking for
Karen
