Does Buddha go to Naraka (hell) to save those tormented beings?
As far as my study in sutta, Buddha did not go to hell to help beings in that world.  They are considered to be "unfortunate" beings; among animals, hungry ghosts, and gods in arupa world because they do not have the strength or what it takes to understand dharma.  However, in one instance, Buddha was so kind to a Naga (which considered to be a being in animal world) by telling him to observe 8 precepts on Upasatha days and he would become human faster.  In one sutta, Buddha compared beings in hell to be like a person drowning in a cesspool not even a strand of hair above it to grab pulling him out.  

For question number 3) not always necessary.  In Migasala sutta, Buddha divided people into 10 groups, which one of them is;


  Here, ânanda, a certain person is overwhelmed with hate and from time to time greed arises to him. He has heard something fruitful, has learnt something, has straightened his view and he personally has gained some release. After death he does not go to loss gains some distinction.