How do you envision the invitees logging in? Must they use the InfoPath form
to log in? And do your invitees all have InfoPath installed on their PCs? Or
must they use a browser to fill out the survey?

The strength of InfoPath is to rapidly create forms (rapid application
development). I cannot say that your scenario lends itself well to rapid form
creation. If you're using the InfoPath client, you can create a task pane so
that user can log in. You can then use a web service to retrieve data for the
user from a data store (e.g. SQL Server database) and pre-populate the form,
and use logic to show/hide questions. If your users do not all have the
InfoPath client, you'll have to use either Forms Services in Microsoft Office
SharePoint Server or Forms Server (neither one is free) to allow user to fill
out the survey through a browser.

When taking everything into consideration, it might be easier to build an
ASP.NET application for your survey and use https for secure logging in. But
then of course, it all depends on what tools and skills you've got available.
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S.Y.M. Wong-A-Ton