@DigiLusionist, The thing to understand about Axure (and XD) is they are prototyping applications, great for creating quick simulations or demonstrations of concepts, but not intended for creating full applications. Reading and writing to external files pretty much crosses that line, although some prototyping tools are much more code-based, like Framer or Visual Studio and they may support external file I/O. With Axure, your best approach would be to copy the content of those files into your prototype, via repeater tables and global variables.
Yes, take a look at the many examples posted on this forum: Search results for 'random' - Axure Forums
You can also use javascript injection to call your favorite or custom rand() function.
No, reading from files isn’t supported. You can (in the editor) paste the text lines into a table or repeater widget and then randomly select a row and set the text of any widget to the text content of that row. Briefly described in this thread: How to extract data from google sheets and store it to a global variable? - #4 by JonB
No, not unless you can use javascript to achieve this, write that into a function and call that via javascript injection. You could fake this by creating a set of global variables to match those in your JSON file.