I found some material which deal with this subject, however I believe that you should make some adaptations in your questionnaire, Is it possible? About the ideal sample-size, it's depends of your purpose, but within these papers which I sent to you, there are some examples of previous studies about this topic.
For preliminary assessment,The sample size should be 10~15 times of the number of items at least, of course, you should also consider the difference of subjects characteristics.