I always recommend identifying your budget first. Many nutrient lines are expensive so its great to make a decision based on the resources you have. Scheduling depends on the fertility of your soil and whether you use things like compost or compost teas. These additives can help reduce the need to fertilize as much. Most people mix in fertilizers with their water if doing indoor grows. For large scale agriculture it may make sense to fertilize the soil. You can decrease your inputs on a large scale by using things like chicken manure and fish emulsion sprayed over soil before planting. Your local grow stores are fantastic for recommendations on brands. Some that I am familiar with are Botanicare, Fox Farm, Cyco, Hydrogarden, Dr. Earth, Age Old. There are so many product lines to choose from. Building soil and understanding soil health are a valuable skill in farming and I suggest reading as much as possible on these subjects. Farmers are much like cooks, I have never met one with the same recipe!