To make the chart full screen, you'd have to detect the window size, then use those dimensions to set the width and height of the chart before drawing it. Here's an example using your code (with a little extra help from jQuery; AJAX removed):
http://jsfiddle.net/jjNWr/
You can add new data to a DataTable object at any time; if you enter a value of null, then that data point will be omitted from the chart.