new to add questionnaire with paypal purchase

as you can see here i added a bunch of paypal links to my site so people can purchase different levels of membership: http://www.goldcoastchamber.com/wordpress/?page_id=48

however, when someone applies for membership, i also need to require that they fill out a short questionnaire about their business.

how do i work the questionnaire into the flow? should it come before or after the paypal purchase? whats the best way to set it up? thanks!