If you post on this forum with more detail what you would like to accomplish with the merge function, you can get advice from users here who have experience with the feature.
I have a book template (124 pages). We fill the book on specific spots with texts and images that come from a survey. Afterwards I want to export these personalised versions as a PDF of a FXL ePub.
Does this help?
... as a PDF or a FXL ePub.
Remember that datamerge is mostly intended for typical corporate supports such as business cards or letters. Of course creative people have from time to time extended the use of datamerge and maybe eventually you will get your project covered this way.
But if your layout has a very peculiar structure, datamerge may simply not fit.
Only a screenshot and a csv sample could help state it for good in either a positive or negative way.
I'm not sure Data Merge is what you want for this.
There are two sorts of merge actions throughout the book: some images and texts.
Here is an online sample version it (not yet final): https://goo.gl/V2UxAM.
On the cover, page 8, page 25 and page 17 (blue icon) you see some of the inserted content.
I hope this helps a bit showing what I'm looking for.
I would rather consider Scripting or XML if the requirements is only to put some contents at some point within a book. I already worked on such customized books and the solution is generally a combination of either CSV and XML ( for the data ) and Scripting for population.
That's worth for simple project like this but for complex projects I would advise automation plugins.
In all cases, no datamerge here unless you are ok with a multistep process.