Is Chanukah a Rabbinical or Biblical holiday?
There are opinions which rule that all holidays instituted to commemorate a miracle of G-d have Biblical status, and hence they rule that the commemoration of Chanukah and Purim are of Biblical origin. Nevertheless even according to this opinion the form of how to commemorate the miracle is only Rabbinical, and hence the lighting of the candles and other matters involved in the form of commemoration are Rabbinical according to all. Nevertheless even these Rabbinical forms of commemoration are of Biblical origin, as the Torah commands one to adhere to the words of the Sages and not swerve from their words.
Reason why Chanukah is not mentioned in the Mishneh:
The Mishneh was written by Rebbe Yehuda Hanassi which was a scion of the house of David. The Chanukah miracle took place with the Chashmonaim which were from the tribe of Levi. Due to that they took over the sovereignty and kingship of Israel after the war, and stole the kingship from the Davidic dynasty. This proved detrimental to Yehuda Hanassi and hence through Divine spirit the miracle of Chanukah was not mentioned in the Mishna.
How many candles are lit in total throughout the days of Chanukah and what is its significance?
In total one lights thirty six candles. This corresponds to the thirty six hours in which the Or Hagnuz was lit for during the time of Adam Harishon. Alternatively it corresponds to the thirty six Tractates of Gemara that the Yevanim desired to annihilate with their Kelipa that was represented by the thirty six cards introduced in those times.
Why in the Diaspora do they not keep 9 days of Chanukah?
Being that Chanukah is a merely Rabbinical holiday, therefore we are not stringent to require the people of the Diaspora to keep an extra day as is required by the Biblical Holidays of Sukkos, Pesach and Shavuos.
Segulos during Chanukah:
- The days of Chanukah are an auspicious time for those women that are barren to have children.
- At the end of Chanukah the gates of Teshuvah that were opened in Elul are finally closed. Until the end of Chanukah there is an extended hand stretched from heaven waiting to accept all those that repent, just like during the ten days of repentance.
- The start of Chanukah marks the end of the Chasima of Hoshanah Raba. It is by Chanukah that the Divine benevolence decreed on Rosh Hashanah finally begins to shine.
One is to increase in giving charity during Chanukah. Giving charity during this time is a Segulah for rectifying different spiritual blemishes.
Cards may not be played as they contain great impurity.
 Chasam Sofer Yoreh Deah 233; According to all Lighting the candles is one of the 7 Rabbinical commands.
 However if one passes the Holiday without performing any form of commemoration of the miracle then he has transgressed a Biblical command according to this opinion. [ibid]
 Shabbos 23a; Admur 158/16
 Taamei Haminhagim 847 in name of Chasam Sofer
 Taamei Haminhagim 849
 Bnei Yisaschar [appendix]
 Abudahrahm brought in Taamei Haminhagim 864
 Bnei Yisaschar
 Taamei Haminhagim P. 363 towards bottom in name of Bnei Binyanim, Reb David Mirimnov, in name of Bnei Yisaschar
 Taamei Haminhagim P. 363 towards bottom in name of Reb Ahron of Zhitmor
 Playing cards is a grave sin as each card contains an unmentionable degree of impurity. [Kedusha Levi Mikeitsz]