On the issue of who is a Gadol:
I think that “Gadol” is short hand for “Gadol BaTorah u’Mitzvos.”
If a person is fluent in Shas and Poskim and has demonstrated the ability to be maiven davar m’toch davar and apply his (or her) learning to real life situations, then that person is a Gadol baTorah.
If a person is meticulous in mitzvah performance, both bein adam l’makom and bein adam l’chaveiro (and l’atzmo), if he (or she) is constantly searching out mitzvos, then that person is a Gadol baMitzvos.
However, practically speaking a person will not be, and should not be, considered a “Gadol” until he (or she) is accepted as a Gadol baTorah u’Mitzvos by other people.