if not autos then you should allow them to start to fill the pot with roots before up potting them. do you have any tap toot out of the bottom too?. this could also be a good indicator. On feeding them , i ould wait until around the 3rd or 4th set of paired real leaves. The two small rounded ones are generally the seedlings 1st meal and designed to avoid starvation while the tap root find water ect. The one that has yellowed could be the seed itself if the others are in the same soil mix. it can happen that a seed will only germinate so far and keel over but the green showing is telling a different story. stick with it but watch your ph when you water them, 6.9-6.2 ideally. good luck with your grow . enjoy the experience.