set cookies or let system know a user has been on site

I don’t think sending your user off site is the best handling in the first place. I would honestly just use Gravity Forms and use the User Registration Add on – if you are already paying for your plugins. It just seems to weird to me to send your user offsite to register, but I’m probably missing data and it doesn’t look like wufoo has User Registration integrated.

You can create two page templates for home (one for registered users and one non-registered users) and add a WP Redirect https://codex.wordpress.org/Function_Reference/wp_redirect that sends them to the approiate page depending on if they are logged in or not.

For added functionality you can use this free little plugin to auto-login users once they have registered and hide the admin bar from them. https://github.com/cameck/Gravity-Forms-Auto-Login