This sort of diet is commonly known as vegan . Volumes of studies point to the negative and positive effects of all sorts of diets, from frugivorous to carnivorous. I am not a scientist and I am growing tired of defending my lifestyle, so I will not attempt to present a comprehensive proof of the efficacy of a vegan diet for humans. You will have to decide for yourself, of course, whether or not you agree with my conclusion.
Breast milk is consumed at a time when humans are growing most rapidly.
Amounts much greater than that will be wasted. You can look up the nutrient composition of these and any other common food items in the USDA nutrient database . Many plants have less of one or two of the essential amino acids. There is no need to intentionally combine them to make up the deficit. Eating a variety of foods will do the job.