Well, I didn't get any replies back then, so I just went ahead with whatever I had.
FWIW, here's my seed starting mix recipe: What I've been using is my own unsterilized compost sifted with a double layer nursery flat basket (1/2"~1"), play sand out of the kids' sandpit (it's surrounded with cut up tree stumps. They decay over time and are replaced. I get the sand mixed with crumbled decayed wood), and my Good Under The Wood Pile Dirt (I've explained this at length elsewhere). I sift with 3/8" riddle and mix them all together. I've used this mix for flats, soil blocks, and paper pots. For up potting transplants, I add to the mix soaked/swelled/crumbled alfalfa pellets for extra N as well as a dolomite lime, greensand, and rockphosphate.
So far, everything has been growing well. I think the high level of biological and mycorrhizal activity is actually helping. No mold, no damping off. I do get a lot of weeds, which I pluck out with tweezers when I inspect/water the seedlings. I'm also getting a whole bunch of critters -- earthworms, millipedes, centipedes, nematodes, pillbugs, spiders, some kind of gnats. So far, there hasn't been any noticeable damage. I remove pillbugs and millipedes because they creep me out, but I've left the centipedes to patrol the seed flats and earthworms to tunnel around and cast.
I just removed a fat nematode out of the tomato flat because I wasn't sure if it was friend or foe, but I generally leave the thread-thin newborns alone.