You have about 40 PAR in there. No way I'd use more than 7 hrs of light till you get the CO2 going. Java Fern and Anubias are low light(less than 35PAR) plants and need shade if in higher light. That is a very large Java Fern. They mostly come/w 3-5" leaves but do get that big eventually.
I do not know the light requirements of the Hygrophila Pinnatifida. So best you find out what it is. Then if it is higher than the Anubias and JF you can move it.
You can place a piece of fiberglass window screen between the light and the top of the tank to shade the JF and Anubias if the Hygrophila Pinnatifida are moved if it requires more light. Or it may be to your liking to let the Hygrophila Pinnatifida replace the Java Fern. But for the JF and the Anubias something has to be found to shade them or they will get thick coats of GSA(green spot algae,the same kind seen on the glass) on the leaves and die. DHG loves CO2 BTW.
As for ferts, store bought liquids are a serious waste of money and made strictly for convenience. In the 500ml bottle($5.99-to even higher)you get one tsp of whatever nutrient it is. In dry ferts you get 1/2 to 1 LB of it for the same money or a little more depending on which kind.
You don't "have to have" but a plant only can take in so much nutrients. Using them in the water cuts what they take from the sub you have making it last longer.
But if that tank is only 20g then a 500ml bottle of Flourish Comprehensive will last you
almost a year anyway. But it is incomplete. It has no Potassium or Phosphate.
API Leaf Zone has iron plus Potassium. Tetra Pride has Potassium and iron.
Look under additional info on that one above.
But all of these products are so diluted that most who use them suggest you use 2 x the recommended doses.
Do not confuse Sea Chem Flourish comprehensive/w Sea Chem Trace. Trace is for fish health. Look at this link to see it.
And this one to see there are others but all for fish.