Yes, you can start from 4 months to give a teaspoon of baby rice cereal but most of the time, he/she will not like it and hasn't learned how to swallow solid food. Thus the tongue will push the food out instead of moving it inside for swallowing. You could try to give cereal at 5 months or so.
Baby should recognize people like the parents or caretaker, by their voice, smell and appearance. Baby might start to cry with strangers around 5-6 months old.