1a. Depends on what they you are growing in, how big the plant is, and how big the container is.
1b. Dr earth, yucca extract, ewc, mycos
2. HLG or nothing.
Pick a nute line, follow their instructions for the stage your plants are in. Resist the temptation to add "extras" . Remember, more is not always better.
Edit: As said above, you can't go wrong with HLG lights.
If you can’t afford HLG lights I suggest checking out Phlizon. Free shipping in the continental US snd Canada (but not Alaska!) and extremely affordable. I’ve been using their 640 watt bar LED for 2 years and it produces. Hard to beat for $399. All diodes still work. Zero problems with this light.