Secure documents etc

[Aaron Silver]

Hello colleagues and friends!

Looking for some advice. I have a client who wants me to build something into their WP site that can do the following:

• customer can log in (after an admin creates their account)
  
• customer is walked through a form that asks them questions and keeps track of what they have and haven't answered; can come back later to complete.
  
• customer can upload confidential documents (tax forms, payroll) to a secure area (ideally the form knows if they've uploaded certain documents or not and keeps track of what they still have to do)
  
• documents are automatically copied over to a client folder in Google Drive
  

I figure that I can probably cobble together something with Gravity Forms and some custom programming, but I'm wondering:

a) if there's a pre-existing plugin that would be a better starting point,

b) if the wp-content/ dir is really secure enough for such documents to be stored, and

c) what am I missing.

Thanks for anything you can tell me!

Aaron.