I was asking myself those questions a year ago and I still don't have all the answers. You received some bad advice on soil from your friend. Its not life threatining unless there is a pest or parasite of some type in it. Not worth risking for a couple of bucks for good soil.
You need to read some cfl journals and start formulating your own plan. As the man said we can help you if you can give us some details. Size of space available, etc.
Let me ask you a question. If you kill those two plants, what have you lost? What have you gained? At least you now know haw to germinate a seed, plant it, and get it to start growing, so you are more experienced than you were a week or so ago, Right? So relax a little. Make your second investment, after getting better lights, a moisture meter.
Overwatering is the biggest newbie mistake. The way to avoid both under and over watering is to use a moisture meter. Available at Lowes, Menards, Miejer, etc for about $15. NO fertilizers for a couple of weeks, which give you time to read a lot. You will find that is ok to make a mistake as long as you learn from it, so you don't make it twice. VV