As for nutrients, i am currently looking at switching to something from the GH Flora series, which seems to be the go to for beginners, so no recommendation there. You definitely do not remove the plants from the rockwool cubes, you just put the rockwool cube into the system and fill around it with the clay medium.

okay got it, thanks. Is the liquid nutrient just placed in the largest tank with the approximate amount of water?

Yes, but look at the directions, because there is an order that you have to follow when mixing. Each nutrient has to be diluted in the main reservoir before adding the next. Also, the nutrient amounts are often overstated, so you can dial them back a bit, no need to start with full strength.