What is 'Pituy'?
Rashi: Seducing - talking someone into doing something.
Ramban: Slyly convincing someone to carry out one's wishes - either via words, money or lies. 1
Though it can also refer to convincing him (her) honestly (See Ramban, who elaborates at great length on the word). Both Rashi and the Ramban claim that their respective explanations coincide with that of Targum Onkelos; the latter adds that it is also synonymous with that of Targum Yonasan.
What is the meaning of "Mahor Yimharenah lo le'Ishah"?
The Ramban maintains that Kesubah is only mi'de'Rabbanan.
With the intention of marrying her, provided the girl and her father agree. See Ramban, who elaborates on the root of the word "Mohar".
Why, according to the Ramban, does the Torah not obligate a Mefateh to marry the girl he seduced and never divorce her like it does by Oneis?
Ramban: Because, since the girl agreed to have relations with him, she is partially to blame, and a monetary Kenas will suffice. 1
See Ramban who elaborates.
Why does the Torah not insert the word "Na'arah" here, like it does by a rapist?
Ramban: It inserts it by Oneis to preclude a Bogeres, whom we might otherwise have thought is also subject to Kenas, since she was raped; whereas by Mefateh, who condescended to have relations with the him, it is obvious that a Bogeres, who is no longer in her father's domain (like a Na'arah is), is not subject to Kenas.