Since it appears from your question that you edit the images for a given wedding shoot in sections, and export each section separately, I can recommend a couple of approaches to do what I think you want. (I don't know what version of Lightroom you're using, nor if the steps below vary that much from version to version, but this is for v5.7.1, which I'm currently using.)
- In the Develop module, select the group / subset of edited images you want to export (i.e., ceremony), right-click on any one of the selected images, and click Export, then Export ... The heading for the export dialog that pops up will identify how many images you're exporting (i.e., "Export 24 Files"). In the File Naming section of the export dialog, select the Rename To: checkbox, then click the dropdown to its right, and select either Custom name (x of y), Custom Name - Sequence or Filename - Sequence, depending on your renaming preferences. For any of the selected options, you can specify the starting number for the sequence in the Start Number: box. At the bottom of the File Naming section of the export dialog, the "Example:" will display what the first of your new filenames will look like, based on your selections. If you select "Edit..." from the bottom of the list of choices in the Rename To: dropdown, you can access even more custom file-naming options.
Re-reading your post, it's possible that you already know how to do the steps above, you just don't want to have to look back to see what the last number of the previous sequence was, to know where to start the next sequence. If that's the case, then I've not helped you, but possibly someone else, so I'll leave my post as is.
- In addition to / as an alternative to the file renaming techniques described above, you could use the Export Location section of the export dialog (directly above the File Naming section) to export each group of selected images into its own subfolder of your destination folder for the shoot.
Hope this helps.
Off-topic: I'm not a wedding photographer, but I'm floored by the 1200-1800 image count per wedding cited by the OP. I'm not surprised that a WP would shoot that many images in this digital age, but I'm amazed that one would have to edit and export that many images after culling. I realize that I'm an old fogie who got married 26 years ago in the dark ages of film, but our wedding album comprises about 65 images, and -- still happily married after all these years, and as an avid photographer myself -- that seems like more than adequate coverage of the event. I don't recall how many proofs we culled from to arrive at our selections for the album, but I doubt it was more than 200. Even if every shot was a keeper, I couldn't imagine selecting more than 100 tops for the final album.