The first thing you need to learn is how to take care of the soil, since that's where the plants get their nutrients. It takes the help of soil organisms to make some of those nutrients available to plants, like probiotics for the human gut if you know about them. There are other things besides the bacteria.
I'm not into lawns, but I know a lot of people use soy bean meal and others for fetilizer, but once again, you need the soil life to help break it down. If you just do an internet search on organic lawns, I'm sure you'd find more info. than you'd want.
There are packaged organic plant foods. I like one called, "Dr. Earth." Home made compost is good and I see you've done the vc, so that's good for the soil and the plants.
Hope that gets you started. I'm sure others will have many more suggestions for you. Keep up the good work!