The createXYLineChart() method will create a chart that uses an XYLineAndShapeRenderer. So fetch the renderer from the plot and cast it to XYLineAndShapeRenderer. Then you can call the methods setSeriesLinesVisible() and setSeriesShapesVisible() to control, for each series, whether shapes and/or lines are drawn for the data items. That way you can use a single renderer and dataset, which makes things simpler.
Your requirement to change the colors depending on another data value requires a little more work. You should subclass the XYLineAndShapeRenderer class and override the getItemPaint(int, int) method. Here you can return any color you want for a data item. The default implementation looks at the series index and returns the color for the series. You need to look at the item index as well, then do a lookup in your table of z-values and decide what color to return.