It's a trade off and the fact that this is a standalone Kiosk solution is an important detail.
A modular design--different files for the two types of data makes for easier updates and more complex management of security as you have to set up security in every such file.
Usually the reason we separate out images (or even any other file attachments) is that it can take up a lot of space in a FileMaker file, which is harder to backup or move the file.
If the file(s) is local (and not on the server) then it may be good to split for updates, because it doesn't have the extra file size to transfer.
If it is hosted on the server, then either could work, but one file may be actually easier to keep updates.