@Jofis,you just listed the three main nutrients in soil (abbreviated NPK) as well as the minor minerals. If it sounds like its a little because its in 50L of soil, its worth keeping in mind that nutrients are often dosed at rates like "1 ml/L" or "0.5 gram/L" (two actual examples from my last grow).
So your soil is already fertilized and to a degree that it may be "hot" - once it gets big enough to start up-taking water, you may find nutrient burn from soil that has too much fertilizer. Or you may be fine. That's another reason to add nothing for 3 weeks: if your soil is "hot" (too fertilizer rich), your going to see the nute burns from it within the next 3 weeks and you'll know its your soil. If you add nutes now instead and get burn, you're not going to know what caused it and its going to be worse.
I would decide on a nutrient brand, pick the base nutes, and feed at half strength beginning on day 21 and stay at half strength but follow their regimen. A lot of people over complicate this and wind up with nute burn, lockout, and single digit harvests to show for it.
I grow in a tent, under an LED, so I can't answer questions about sunlight as I've never tried it nor researched it and the methods aren't quite the same (unlike the sun, my LED is stationary, for instance).
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