no first place, no last place

Zos chanukas ha'mizbeiach b'yom himashach oso... (7:84)
...Zos chanukas ha'mizbeiach acharei himashach oso (7:89)

"B'yom" or "acharei" -- which one is it?  

The Midrash (Netziv as well, but also see Rashbam) explains that even though it took 12 days for the Nesiim to complete the process of offering their gifts, one per day, and only after -- "achrei" -- day 12 was the chanukah complete, since they were all equal in merit it is as if they all brought the gifts on day 1, "b'yom himashach oso."

The yesod here is that these were not 12 separate individual gifts, each of which stood alone, but rather these gifts of the Nesiim were 12 parts of one whole.  When you are dealing with multiple things, then there is a first, a second, a third, etc.  Not so here when we are dealing with one thing -- one gifts, 12 parts to it.  

We see the same idea earlier in the parsha when Hashem tells Moshe "nasi echad la'yom naso echad la'yom yakrivu es korbanam" (7:11 - easy pasuk to remember).  Netziv is medayek that the tense is wrong.  Since the pasuk is speaking about the individual nasi, it should say "yakriv" in the singular, not "yakrivu" plural.  He answers:

 אלא בא ללמד דנשיא אחד ליום יקריב בשביל כולם, וכמו שכולם מקריבים בכל יום משנים עשר יום. 

One person may be doing the offering, but he represents the klal, hence the use of the plural.

Maharal uses this same yesod to explain the smichus haparshiyos of the gifts of the Nesiim to the parsha of birchas kohanim.  The culmination of birchas kohanim is the bracha of "v'yaseim lecha shalom."  The way the Nesiim offered their gifts is a model of how a community built on shalom functions.  On the first day the korban of Nachshon was offered.  The parsha describing his gifts starts, "V'korbano..."  Why the extra vav here?  This is the first pasuk in the description of the first gift -- what came beforehand that we need a "vav" to connect it to?  Maharal (in Gur Aryeh, see Midrash Rabah 13:11 for a different answer) answers that the Torah is teaching us not to look at the 12 Nesiim in linear heirarchical fashion, where there is a first in line and a last in line, but rather to look at the 12 as a circle, where there is no beginning and there is no end. We start with a "vav" because the beginning connects to the end, and the end connects to the beginning.  When each individual acts "b'shem kol yisrael," then there is no individual in first place or in last place.

2) The famous smichus ha'parshiyos issue the Midrash, the Ramban, and others deal with is the connection between the gifts of the Nesiim and the lighting of menorah by Aharon that follows afterwards in next week's parsha.  What is overlooked is that there is another pasuk in between those two topics (7:89): 

וּבְבֹ֨א מֹשֶׁ֜ה אֶל־אֹ֣הֶל מוֹעֵד֮ לְדַבֵּ֣ר אִתּוֹ֒ וַיִּשְׁמַ֨ע אֶת־הַקּ֜וֹל מִדַּבֵּ֣ר אֵלָ֗יו מֵעַ֤ל הַכַּפֹּ֙רֶת֙ אֲשֶׁר֙ עַל־אֲרֹ֣ן הָעֵדֻ֔ת מִבֵּ֖ין שְׁנֵ֣י הַכְּרֻבִ֑ים וַיְדַבֵּ֖ר אֵלָֽיו׃

The Torah sticks in a description of Moshe entering Ohel Moed and hearing the dvar Hashem.  How does that fit in?

The classic answer for why the parsha of lighting menorah appears here is because Aharon was jealous that he did not get to contribute something with the Nesiim, so Hashem revealed that his job of lighting menorah is a greater prize.  Alshich explains that this pasuk describing Moshe speaking to Hashem in Ohel Moed comes to address the question of why only Aharon felt left out -- why didn't Moshe feel left out?  The Torah therefore reminds us that Moshe heard Hashem's voice speaking to him.  He did not feel like his not bringing a gift in any way diminished his closness to Hashem.  (I would have said that only Aharon as the leader/nasi of Levi felt he should have been included.   Moshe was not the nasi of any particular sheivet.)

Tzror Ha'Mor offers an explanation (see Seforno as well) that also addresses the question we started with or "acharei himashach" vs "b'yom himashach":

וחזר לומר זאת חנוכת המזבח אחרי המשח אותו כדי לסומכו לפסוק ובבא משה. להורות שהחנוכה הראשונה היתה ביום המשח אותו באלו הקרבנות. והחנוכה השניה היתה חנוכת השכינה לדבר עם משה. כי תכלית המשכן ואלו הקרבנות לא היה אלא להוריד השכינה לתחתונים. וזהו אחרי המשח אותו. כי החנוכה הראשונה היתה ביום המשח בענין הקרבנות. והחנוכה האחרת שהיתה אחרי המשח אותו. היתה זאת ובבא משה אל אהל מועד לדבר אתו וישמע את הקול מדבר אליו. וזה להורות במעלת משה שהשיג עתה בחנוכת הנשיאים מה שלא השיג עד עתה. והוא כי פעמים אחרות כשנכנס משה היה ממתין עד שבא הדיבור אליו. אבל עכשיו בבא משה וישמע את הקול. שכבר היה שם השם ממתין ומדבר. לפי שזה המקום אוה למושב לו. 

As we've discussed in the past, there is a dual function to the Mishkan.  The mitzvah to build a Mishkan, Rambam writes in the beginning of Hil Beis haBechira, is to make a place where korbanos can be offered.  Ramban in many places takes a different approach and writes that the Mishkan was the place of revelation, a duplicate of Har Sinai.  Corresponding to these two roles we have two chanukos.  We have the chanukas haNesiim "b'yom himasach oso" which was done through the korbanos that they brought.  Secondly, we have "acharei himashach oso," after those offerings were completed, "b'vo Moshe el Ohel Moed...," a second chanukah done through haShechina, revelation. 

The Tzror haMor ties these two chanukos together.  It is the offering of the korbanos of the Nesiim which transformed the Mishkan into a place that would also serve as the focal point of Hashem's revelation.  The second chanukah is not independent, but goes hand in hand with the first.