While the Torah may or may not be in one-for-one in format of a Ketubah, there are many similarities between a Jewish wedding and when the Israelite received the Torah. In this "wedding," the Torah would take the place of the Ketubah and this would be a basis for understanding the Torah as being a Ketubah. What is important to remember however is that the Jewish marriage ceremony seen at weddings now is vastly different than the ceremony that was used by ancient Jewish peoples. First understanding how the ceremony used to be performed is necessary, and then you can better understand how the Torah takes the place of the Ketubah in the marriage of God to Israel.
The first part of any historical Jewish Marriage was the Shiddukhin (שִׁדּוּכִין). This was actual betrothal at which a bridegroom or his family would negotiate the terms of a marriage with the bride and her family. It was at the Shiddukhin that details such as the Mohar (מֹ֫הַר) or bride price were decided, when and how it was to be paid and and details such as where the bride and groom were to live after marriage, what happened in the event of infidelity on behalf of either party, what happened in the event of the death of either party before or after marriage, and/or before and after children and any other details or terms the bride, groom, or their respective families saw fit to include as terms of marriage. This was all traditionally recorded as a contract knows as the ketubah (כְּתוּבָּה).
If we are to understand God as being wedded to Israel (and/or Christ being wedded to the church), then the first recorded instance of the Shiddukhin would be in Genesis 15 In this passage, we see Father Abraham, the father of Israel negotiating the terms of the marriage and making a formal commitment to these terms. The exact Ketubah, would then be recorded in 15:18-21.
The next part of any betrothal is the Eyrusin, the actual engagement period. In terms of The Bible\Israel this would be be the period from Genesis 16 to Moses.
Next in a Jewish wedding ceremony is the actual wedding itself - the Nissuin (נישואין). As with any wedding, the first thing any good bride does is gets ready for the big day by washing herself, then applying makeup, doing her hair and nails and getting dressed. This custom is as old as marriage itself. The first thing in that sequence though, is the bride washes herself. This has actually been internationalized in the Jewish wedding ceremony and is known as a mikveh(מקווה). This is not exclusive to the Marriage ceremony and mikvehs are used many other times as well, but is certainly a part of the big day.
If we are to understand the the Torah given in Exodus as the Ketubah, then Exodus 19:10-15 must be the mikveh performed by the LORD's bride. In this passage, every person in Israel is ordered to be consecrated and wash in preparation for something.
Unlike today, ancient people's did not have a telephone and the commencement of a marriage was rather... abrupt. Typically, the wedding would begin whenever the terms of Ketubah were satisfied. This might be once the bride price has been saved up, once the bride and grooms home was complete or some other condition was satisfied. Because the bride never knew when the wedding would come, "the bride and her bridal party were always to be ready - this is the background of Yeshua's parable (Mat. 25:1-13). It was customary for one of the groom's party to go ahead of the bridegroom, leading the way to the bride's house - and shout - 'Behold, the bridegroom comes.' This would be followed by the sounding of the Shofar." (שופר) or ram's horn.
In Exodus 19:13b, the Shofar is blown signifying the start of the wedding ceremony.
At any Jewish wedding there is a Chuppah (חוּפָּה), a type of covering or canopy. There is a great deal of rich symbolism in the Chupppah which I will not go into here, but it is interesting that Exodus 19:16-17 records a thick canopy or covering of cloud on Mt. Saini which the Israelights stand under. Traditionally, the bride and groom stand under the Chuppah at the altar during the marriage ceremony.
Next, in any Jewish wedding, the Ketubah is read aloud and the bride and groom reaffirm their agreement in front of all the witnesses present at the wedding. Likewise, in Genesis 20-23 we have the 10 commands followed by the Law read to Israel. In Exodus 24, the people or Israel then affirm their Covenant with God.
During the wedding, it is traditional for the bride and groom to recieve 7 blessings. This was known as Sheva Brachot (שבע ברכות; the seven blessings) or birkot nissuin (ברכות נישואין; the wedding blessings). Likewise, in Exodus, there are 7 Passover blessings given in Exodus 23.
Of course, the best part of any wedding is the reception and if the Israelite knew one thing, it was how to party. A large part of any reception is that a meal is shared by the guests. The marriage of Israel is no exception and In Exodus 24:11 it is recorded that the 70 elders of Israel share a meal with God after the wedding.
Being the party animals that they were, Jewish wedding receptions historically would last for 7 days and wedding guests would party with them during this time. The reception would typically take place at the bride and grooms house or there was a tent nearby and in the evenings the bride and groom would retire to this place, or Chuppah (I told you there was a lot of symbolism here) to do what newlyweds do.
Likewise, Exodus 24:15-16 records that Moses goes up into the canopy of cloud cover for very intimate time with God. This is a 7 day period during which The Bible states that "The glory of the Lord rested on Mount Sinai." This represents the consummation of Israel's marriage to God.
This only serves to highlight the depths of Israel's betrayal recorded in Exodus 32. The wedding is barely over and Israel is already cheating on God a mere 47 days later. This only serves to highlight how poorly Israel continually treated their bridegroom and how forgiving He is and makes Israel's infidelity all the more heartbreaking.