The Shulchan Aruch (in Yore De'ah סימן רמב - שלא להורות בפני הרב, ודין רב שמחל על כבודו) discusses greeting one's Rav - and mentions that one doesn't greet him as one does any other person, and possibly one shouldn't greet him at all.
טז לֹא יִתֵּן שָׁלוֹם לְרַבּוֹ וְלֹא יַחֲזִיר לוֹ שָׁלוֹם, כְּדֶרֶךְ שְׁאָר הָעָם, אֶלָּא שׁוֹחֶה לְפָנָיו וְאוֹמֵר לוֹ בְּיִרְאָה וּבְכָבוֹד: (שָׁלוֹם עָלֶיךָ רַבִּי, וְאִם נָתַן לוֹ רַבּוֹ שָׁלוֹם, אוֹמֵר לוֹ) שָׁלוֹם עָלֶיךָ מוֹרִי וְרַבִּי. וְכֵן נוֹהֲגִין. וְיֵשׁ אוֹמְרִים דְּאֵין לְתַלְמִיד לִשְׁאֹל בִּשְׁלוֹם רַבּוֹ כְּלָל, שֶׁנֶּאֱמַר: רָאוּנִי נְעָרִים וְנֶחְבָּאוּ (אִיּוֹב כח, ט) . (יְרוּשַׁלְמִי הֱבִיאוֹ הַגָּהַת מַיְמוֹנִי פֶּרֶק ה' וְכֵן כָּתַב תא''ו נָתִיב ב' וּבֵית יוֹסֵף בְּשֵׁם רַבֵּנוּ יוֹנָה)
16: One should not greet one's teacher nor return his greeting the way one does with other people, instead one bows towards him and says - with awe and respectfully: ("Shalom to you, Rebbi", and if one was greeted by him first, one replies) "Shalom to you my teacher and Rebbi". And this is the custom. Some say that a student should not greet his teacher at all, as it says (Iyov 28:9) "The lads says me and hid".
So casually saying "hello" could be a problem.
As to his title - that would depend on local custom. In Sephardi circles the Rav is titled "Chacham", in Yeshivish circles it's either "haRav" or "Rosh haYeshiva" and in many circles a Rabbi is addressed in 3rd person, as in "I didn't understand what the Rav just told me".