I recently bought 4 cultures and two of them appeared to mold and die. I am learning, did I do something wrong?
Generally, mold is a sign that the cultures dried out. Try keeping the cultures at about 60-70% humidity, and/or adding just a bit of r/o or distilled water at the first signs of mold.
When it's time to feed? Any day from 14 to 28? When is it time to make a new culture?
How normally I would calculate how many cultures I need peer week?