Good move buying soil, soil from outside has insect larva and nematodes etc. that will punk your seedlings.
Also, rootmass certainly effects bud yeild. I would go with the largest pot you can utilize. You can really pump up buds with fertilyzers but you run the risk of getting bleck, wont burn product.

Also, cut whatver soil u use with 20-30% perlite.

learn about ferts, 202020 for veg, and the various bloom mixtures.

Foil can cause hotspots, but I don't know if you can use it.


Good luck!