Don't worry too much, we have to make mistakes in order to learn. Many of the soil company's do light mixes for seedling but I've never used any. I just put my seeds straight into whichever soil I'm using for that grow and off they go. I'm currently using Biobizz allmix but it's the same with FFOF and Canna professional. Like Bobby said, usually you won't need to feed for the first month but somtimes I like to start adding very small amounts after the first few weeks just to be ready for when the plants suddenly decide they are hungry