I would not send my customers a questionnaire. I do not want to fill out customer satisfaction surveys myself so I would not ask it of my customers.
If I were you, I would send the kick off letter and invite them to contact you with their questions and comments. I would also make the time to call many of them to discuss their needs. If they want< meet with them at their home and walk the property and discuss what they want. Take good notes and deliver.
Good luck and do keep us posted on your progress.