I believe what I should do then is create an array and a json within the construct, use Ajax to import the json into the array
If you need to pre-load some data into the array, then yes - create an array file in the project and load it with AJAX. You don't need NWjs for this part.
and then use NJWS to write the array into the json, right?
If you need to save the contents of the (changed) array in runtime, you can either save it to local storage or write to a disk file with NWjs.