all our problems | Container gardening | Commercial Hydroponics farming

Good thread to post my questions on container gardening. 

I have sowed some Zinnia and some Double balsam seeds in a seeding tray with only (well rinsed and drained) coco-peat as medium. I used 2 seeds per hole. Placing them 1/2 inch from the top. Watered them mildly and covered them with a transparent sheet and sealed them to retain moisture. I did this on Saturday and on Monday I couldn't resist so peeped to find some seedlings germinate. On Sat and Sunday I kept them in the sun for a few hours. Now I have kept it in a bright area but not in direct sunlight. Its summer hence I am guessing that's helping them germinate quicker. 

Now here are my questions – please correct if I am wrong. 

As per GG, now I need to wait till the seedlings germinate well and some leaves appear. As soon as they germinate I need to remove the Plastic covering sheet and slowly introduce them to outer world. Now what does this mean?

- Once I remove the plastic sheet, do I need to keep them indoors with few hours of light/ sunlight ? 

- Or do I need to keep it in light indoors? 

- How long/ tall shall I wait for the seedlings to grow in coco peat medium before I can transplant them? 

- What should be the medium in the container? I will be using plastic pots or plastic containers. Will just coco-peat be enough for the plant to grow? I have well cured cow dung as well as vermi compost. The shop owner told me to use Vermi Compost/ Culture only a handful per pot 12". Not in a 1:1 ratio. 

- I got something call BOOM FLOWER  and some root growth enhancer. Which one do you think I could use and when? 

- After how many days of a transplant and at what plant age shall the fertilizers be added? Is it different for different plants? 

- Should root growth enhancer be used only for grafting? or while planting cuttings? 

- I can't understand N-P-K of different varieties. Does 15-15-15 come in a diff bottle than 20-20-20. Do they come in 1 bottle or 3 bottles? I understand the concentration is 2-3 ml per liter. Sorry, these might appear as noob questions, but don't know anything about fertilizers.

- I have 2 pots of lemongrass, one is doing very well and has developed multiple stalks with many leaves and looks healthier. However, the other is barely growing. Very few leaves and not much growth. A few days back I saw red ants had dug holes from the top. And also found them in the roots. I don't know if they affected the roots or just entered the soil?

Please help. 

Thanks GG for the prompt replies. 

Any tips you could give for my lemongrass which isn't growing well? its got the same soil and same growing conditions of temperature water etc. But one is flourishing and other is not. Could red ants really be a culprit?