Help, first grow

Wait until your plants are about a month old and a 20-20-20 is too strong so when you do feed do it at 1/2 the nutes it calls for. Your yellowing looks like overwatering also check your ph it shouldn't be over 7.0 anywhere between 6.5 to 7.0 is good.

Dude, its the first set of real leaves, its ok it dies. Dont worry.

As for your nutes, if you want good weed, get your lazy ass off the computer chair and buy some better nutes.
Honestly, if you cant do this, then I have no pity for you and your plant.
Remember high N, low PK for veg. Too much PK can cause burning of leaves.

I'd wait 1 month and do 1/4 strength.