Id like to know, emotionally and psychologically what to expect from a boy whose father died when he was very young.( about 3 yrs old)

Hard to know... some will depend on the rest of his childhood. How loved and taken care of he feels... but there may be some sense of abandonment that could crop up later in life.

It also depends on the role of other men in his life. With positive male role models and the child coming to terms with his father's passing, the scars could be minimal.

What was the other factors, who else was there for him, who else helped in the over all family.

Yes but also a lot of frustration. Remember a child of 3 does't understand what death is neither why. So he will feel deceived and abandoned by his father in a way or the other.
There will be a lot of events in his life where he will miss the parental presence and that can be shown through reserve or anger.
Anyway it depends on the family support .There is a lot of work to be done here. Good luck.