Overall score for questionnaire data

Hi All,
My psychology survey measured several technology related stressors (techno-overload, techno-complexity, techno-support, etc.) and included sub scales taken from several sources in the literature, so it is not in itself a single validated questionnaire. However, I wanted to calculate a "total technostress score" by adding up the subscales. How would I go about validating this total score? I have conducted Cronbach's alpha on the total score and it is good >.80. What else would I need to do to confirm that summing the sub scales is an appropriate thing to do?

Any direction would be greatly appreciated.

Thank you