Why does the Torah repeat the Korbanos of each Nasi? They were all identical? Why did it not present the details of Nachshon's Korban, and continued "v'Chen Hikriv ... " for each subsequent Nasi on his day?
Ramban (2) #1, Moshav Zekeinim (84): Hakadosh-Baruch-Hu confers honor upon those who fear Him. Consequently, bearing in mind that all the Nesi'im thought to bring their Korban and to inaugurate the Mizbe'ach simultaneously, and that it was impossible for each Nasi to be the first to bring, Hashem honored all of them by repeating all the details by each one.2. Ramban (2), Moshav Zekeinim (84) (both citing a Midrash): Because each Nasi had a different reason in mind - one that was relevant to his tribe.
Ramban (2) #2: Because, based on a tradition that Ya'akov handed down to each tribe what would happen to it until the time of Mashi'ach, each Nasi brought Korbanos that pertained to that tradition. 1
Seforno: To teach us that each Nasi had in mind to atone for the specific sins of his tribe, and that therefore, each Nasi's Korban was accepted individually with goodwill by Hashem. 2
Ramban: Consequently, Nachshon's Korbanos were connected to Malchus, (as we explained - from Pasuk 13 - 18 [in italics]), Yisachar's to Torah and Zevulun's, to Parnasah (See Ramban, DH 'u'Nesanel' and 'u'Zevulun').
Seforno: And each Nasi stood by his Korban akin to the Ma'amados (where representatives of the community stood by the Korbanos Tzibur whilst they were being sacrificed on the Mizbe'ach).
Why does the Torah say "Hikriv" about Nesanel ben Tzu'ar, which it did not do for any of the other Nesi'im?
Rashi (19): Because the tribe of Reuven claimed that, if Yehudah preceded them, they ought to come next, since Reuven was the firstborn. So Moshe informed them that he was merely following Divine instructions - to go after the order of the Machanos, in which case, Yisachar had to follow Yehudah.
Da'as Zekeinim: According to order of birth, Yisachar should not have offered second; they merited to, due to their Chachmah - "Yod'ei Binah l'Itim" (Divrei ha'Yamim 1:12:33).
Hadar Zekeinim: According to order of birth, Nesanel should not have offered after Yehudah. He pushed himself to do the Mitzvah.