I like the whole
Roots organics line, I used to run it when I lived in SD. I do like the soil, it is a coco based soil so it does drain fairly quickly and if you are using RO or distilled water you will absolutely need to add some calcium to your nutrients. But there is a lot of good stuff in that soil blend and it does allow for growing great plants. Personally these days I am using
Happy Frog from Fox Farms and am really liking it. There is enough nutrition in there for young plants without burning them and allows for use of bottled nutrients without over doing it. Either of these soil options are good ones. I am not sure if you went into Mighty Hydro, but they may have other suggestions for you as to which soil they like, its always nice to have another opinion. As for the nutrient line, if you want to go organic Roots is a great option, I am currently running the
Bio Bizz line, but I still use the HP2 and HPK from the Roots line. Of course you can use the worm tea, a once a week application would definitely have a positive effect on your plants. You could also incorporate some insect frass into your routine with a top dressing every 3 weeks. It will kick your plants immune response on and help them fend off pests if they do try and show up in your garden.
There is nothing wrong with only growing 3 plants, but I would say don't plant on anything other than plants to be on the floor of your tent. I try to keep any equipment elevated or outside of the tent to allow for maximum floor and canopy space. Plus if you put a fan or humidifier directly in the tent the plant(s) closest to the unit will get the brunt of either air or moisture you are trying to get into the whole tent.
With low stress training you will forgo any clipping of the main growth of the plant, it is just bending the branches over and tying them into place. You will not inhibit the growth rate of your plants and you will still be able to make the whole canopy more even. Mainlining combines LST and topping, and typically comes out best with plants from seed rather than clone (I am not sure which you are starting with). I started with LST when I first was learning to grow and I am happy I started with that technique as I was impatient and wanted results quickly and topping delays the whole plants process a week or so (at least in my opinion). It also kept me from over stressing my plants before I knew what I was doing. Once you get the hang of growing I would suggest trying all methods of training, they are all unique but aim at getting you to the same place.
Here is a link to my diary thread, not everything goes right, even for someone with experience:
https://www.thcfarmer.com/threads/the-new-project.100894/. It may help you get an idea of training and other issues to note along the way. I hope all this info is still helpful.