Hi there mate first tip I can offer is Don't attempt to feed them yet wait another week and they will appreciate the food and grow accordingly. 2nd Tip try to keep the soil and nutrient feeds in a PH range of 6.2 - 7 this will allow your plant to optimise nutrient uptake. 3rd Tip is for outdoors , Prepare your growing area now and consider some sort of protection for your seedlings to combat animal/pest attack. Try to keep the plants in full sun but away from very windy areas. 4th tip is if going indoors be very careful taking outside soil indoors as you might inadvertantly bring umwanted creatures in as well. (bugs , diseases ) %th tip is for your last question .. It wont hurt the plant if you add a little more soil to those cups which will also help support the plant, just dont cover the leaves with dirt. Hope Ive helped 😃