Why does the Torah write "Hikriv" twice, once here and once in the previous Pasuk?
Rashi: There were two reasons why Yisachar merited to follow Yehudah: Because they were Torah scholars 1 and because their Nasi, Nesanel ben Tzu'ar, suggested to the Nesi'im to bring the listed Korbanos (R. Moshe ha'Darshen in the name of R. Pinchas ben Ya'ir). 2
Shmuel ben David, in Moshav Zekeinim: Nesanel offered what the others did not offer, for he was wealthier. The Targum of "Yisachar Chamor Garem" (Bereishis 49:14) is 'Atir b'Nichson' (rich). He offered what they did not, and also what they did. The Torah did not mention it, lest he get haughty, and to teach that all of them were equal.
Why is "Hikriv" written Chaser (without a Vov)?
Rashi: Without a 'Vav', it can be read 'Hakrev' (a command). Hashem ordered that Nesanel offer this day. (Refer to 7:18:2:1).
Why is Nesnael mentioned before "Nasi"? For the other Shevatim, "Nasi" is first! (Moshav Zekeinim)