R' Tzadok explains that the chanukas haMikdash and the holiday of sukkos are in fact one and the same celebration. The sukkah is a commemoration of the ananei ha'kavod that surrounded Bnei Yisrael in the desert, and when the Mikdash was dedicated, the navi tells us, "V'he'anan malei es beis Hashem," (8:10) that Hashem's anan descended into the place. The ananei ha'kavod of the midbar came in Aharon's merit, and it was Aharon's descendants who served in the Mikdash. Mikdash and sukkah both symbolize the same hashra'as haShechina in Klal Yisrael. Each one of our sukkos is a mini-Mikdash.
The Vilna Gaon writes that the reason we celebrate Sukkos in Tishei and not in Nisan is because the ananei ha'kavod departed after the sin of cheit ha'eigel and did not return until 15 Tishrei when Moshe began collecting for the construction of the Mishkan. In light of R' Tzadok's explanation, it is not coincidental that the clouds returned just then. The kedusha manifest in Mishkan/Mikdash is the very same as was manifest by the ananei ha'kavod.
2. On one of the days of Sukkos I suggested that the shalosh regalim correspond to banei, chayaei, and mezonai. Pesach is the holiday of banai -- the Torah speaks to us of 4 sons. Shavos is chayai -- chayei olam nata b'socheinu, the Torah. Sukkos and Shmini Atzeres is mezonai, as it is on this chag that we daven for geshem, which encompasses our material needs. I found the Sefas Emes alludes to this idea, see 5743 d"h baMishna.
3. The gemara says Shmini Atzeres is distinct from Sukkos with respect to 6 halachos represented by the siman PZ"R KSh"V. R=regel. With respect to what din is it a new regel? I saw quoted in the name of the Rogatchover that there is a new din of chayav adam l'hakbil pnei rabo ba'regel on Shmini Atzeres in addition to the chiyuv of the same din on Sukkos.
4. V'Zos haBracha is the only parsha not read on a Shabbos. R' Tzadok explains that Shabbos is "keviya v'kayma," it's kedusha is set without our having to do anything, unlike the kedusha of Yom Tov which comes through beis din's declaration. The parsha of each Shabbos, the torah unique to that week, comes down to us like the kedusha of Shabbos, from without. We hope that we can accept it and absorb it each week when it comes down to us.
The kedusha of Zos haBracha, after a full year of parshiyos, after experiencing a whole cycle of moadim, is a kedushah that comes from within. At the end of the day, what Torah is all about is not obeying rules imposed upon us from without, but discovering within ourselves that those rules are built into our souls and define who we are.
Sefas Emes explains that the difference between Shavuos and Simchas Torah is that on Shavuos we celebrate Torah sheb'ksav -- it is the Torah given to is, imposed upon us. Simchas Torah, Shmini Atzeres, is torah she'ba'al peh, the Torah that comes from within, that we are mechadesh, that is part of who we are.
5. "Smach Zevulun b'tzeisecha..." Sefas Emes asks: why should Zevulun be happy that he has to go off on business? I don't know about you, but I don't get much simcha out of riding the subway and dealing with hectic problems at work all day. And it's not just about work. This is the last few days of Yom Tov, and then we go out -- "tzeisecha" -- out from an intense period of kedusha back to the daily grind, back to the world of chol. Where's the happiness in that?
Sefas Emes answers that what the Torah is doing here is giving us advice. How can we make that transition back to the world that for better or worse we have to be part of a successful one? By making sure we start off with simcha. If you are a Zevulun and are stuck going out there, then "smach Zevulun b'tzeisecha," before you go, take a moment to rejoice in what you have before you leave. Have a simchas Torah, celebrate the dveikus of the chagim, appreciate the experience. How many people go through three+ weeks of Yom Tov and don't even take a moment to THINK about what is going on? How many people pause to reflect? This is the last chance -- take advantage! Absorb the simcha now, and then it will stick with you, so that even "b'tzeisecha," the Torah will be with you, the dveikus will still be with you.