On the time between engagement and the wedding, the Rebbe's guidance:
Don't prolong the engagement. Once both sides have agreed, set a wedding date promptly and keep the time between the decision and the wedding as short as possible; hastening the wedding is commendable and brings added blessing (IK 9096, 9223, 10041, 10059, 10888, 10913). Ideally it should be under a year (IK 10364). This applies all the more when both live in the same city, for reasons of tznius (IK 10304). Customs of long engagements that have no basis should be reconsidered, unless there is a halachic reason (IK 3560). Long engagements are discouraged, and where there are many uncertainties, one should not proceed at all (IK 10937).
Engagement customs and arrangements. Follow local Chabad custom for the engagement formalities; what matters most is arranging the wedding in good time (IK 5014). Writing tenaim on the day of the wedding is entirely proper (IK 1886). Wedding arrangements, including timing and venue, follow custom and are decided by the parents; communicate directly to prevent misunderstandings, and clarify the practical details in advance (IK 9761, 10492).
Timing in the calendar. Weddings are held throughout Kislev, but not in Teves (IK 6519).