Basically you can make a table from a selected text with the method convertToTable() this way:

var doc = app.activeDocument;                  // your document
var frame = doc.pages[0].textFrames[0];        // first text frame on first page
frame.texts.everyItem().select();              // select all text inside the frame
var table = app.selection[0].convertToTable(); // convert the selection into a table     

Before:

After:

Reference:

• Text object

As for the rest... it's need more details about your workflow. JSON and CSV are quite different beasts, it would be different parsing algorithms for each of the formats. Will you copy the contents of the files manually or the script should read all csv or json files from some predefined folder? Or there should be some interface to select a file(s). Or a folder? How it supposed to handle a page size and formatting of the table? Etc...