Why does the Torah switch from E-lokim to the Name Havayah?
Ramban: HaSh-m is about to inform Noach (in 7: 3) that all the animal world would live with him in the Ark. By mentioning the Name Havayah (the Name that denotes mercy and that is always used in connection with Korbanos 1 ), He is hinting to him that on the merit of the Korbanos that Noach would bring upon exiting the Ark, (a) the entire world would continue to exist; (b) He would never again destroy the world.
What was the point of telling Noach that he was a Tzadik?
Ramban and Seforno: HaSh-m was telling Noach that he alone (and not his family) 1 was a Tzadik worthy of saving the entire world.
Why does this verse omit the adjective "Tamim," which it inserted at the beginning of the Sedra (6:9)?
Rashi: Because one never mentions all a person's praises in his presence. 1
Maharal (Nesivos Olam, Tochachah, Ch. 1 p. 191): Saying all of his fellow's praises appears like flattery. One should, however praise him somewhat to show that he holds him in esteem, to generate love between them.
Having informed Noach that his family would enter the Ark, why repeat it here?
Ramban: In the Pesukim prior to 7:1, which were said to Noach years before the Flood, HaSh-m was telling him what would happen at the time of the Flood. Here, He is giving him instructions a week before the Flood (on the tenth of Marcheshvan).
רש"י: שאומרים מקצת שבחו של אדם בפניו וכו': למה כך היא ההנהגה?
מהר"ל (נתיבות עולם, נתיב התוכחה פ"א עמ' קצ"א ד"ה ואמר): באמירת כל שבחו נראה כדברי חנופה, אבל את מקצת שבחו יש לספר להראות שהוא בעל מעלה בעיניו, כדי להביא אהבה ביניהם.