The scale is visible by default, although if the plot is very big it may be out of bounds.
Try using view-set frame size and entering 150 and 150. This gives a square plot fitting on the page.
There is no way to add the units. I advise doing further annotation in another program.
E.g. if you file-export pdf, the file can be edited in a vector graphics program like AdobeIlustrator or Inkscape.
or file-export svg, file can be edited by many programs and are suitable for presentations. | 
