A lot of people say that Scott's soil is better than Miracle Grow but I mix my own so I'm not sure. Pick up some vermiculite & perlite, I use them both because the perlite can start floating to the surface if you use to much of it. Fox Farm is suppose to be a good soil & fert. but you probably can't find it at Lowes. If your are is like mine you'll have to drive a couple of hours just to find the stuff. You can find out on their website.
here's my soil mix (part of it comes from potpimp)
2 cubic ft. Miracle Grow Organic
2 cubic ft. Fox Farm(not in my area so I found some local organic)
1 cup blood meal
1 cup bone meal
1/2 cup dolomitic lime (raises & stabilizes pH)
1 teaspoon of miraite of potash(switching this to greensand next time)
2 1/2 cups aluminum sulphate (lowers pH)
Wet thoroughly and let it set for a day or 2
If you use this mix DON'T PUT ALL THE ALUMINUM SULPHATE IN AT ONCE Start with one cup let it set for a day and check the pH if it needs to go lower add more if it needs to go up, add some more lime.
yes you can use the mH for your seedlings just keep it a couple of feet away until they are ready for more light.