Images shouldn't be a problem. You could distribute each quest chain as a directory, with all the files inside that it needs. The user would only need to enter the directory name to allow the plugin to find it.
Or, indeed, each quest could be distributed as a self-contained plugin, which includes all the Lua code, so that it would appear as a separate item in the Plugin Manager, and the user wouldn't have to enter any filenames. It's not like this is 1995, when we had to conserve disk space. Plugins are tiny compared to disk capacities.