Database Populate Forms – Customer Data Location

Hello everybody,

I manage a WP 4.1 site for a company with 600+ customers.

In this site, customers can apply for information through a contact form. (I use Contact Forms 7, but contemplate switching to Gravity forms e.g.)
Because customers revisit the site for new info applications, I’d like to help them, by pre polulating the contact form with all available customer data that I stored in a table called wp_customers in the database.

What would the best way to go about this? My instinct tells me not to add all 600+ customers to the wp_users table, or should I?

I’d like to use a solution that’s in line with the WP architecture, so no strange and creative work arounds… 🙂

All help is welcome, thanks in advance!

Bye
Ward