How do you track a potential customer?

You need a CRM app to integrate with QBO.

Hello, @mhorn. 

Tracking customers without adding them in QuickBooks Online (QBO) isn't supported. You may consider using a third-party app to integrate with QBO.

To find an app in the program, here how:
 

1. Sign in to your QuickBooks Online account.
2. Navigate the Apps tab on left menu, then select Find Apps.
3. Search for the app you wish to connect or select the Browse category  to search for an app by category.

For a future guide in sending customer statements in QBO, feel free to check this article: Create and send customer statements in QuickBooks Online. 

You can always go back to this page if you have other customer-related concerns.  I'll be around to lend a helping hand.