Disclaimer : I am not a lawyer, I am only a developer, computer scientist and computers lovers :P
First of all, warn your users what you will store and for what purpose. Example : on your registration page
"Email are stored to identify you and to send notifications if you want to (configuration in your profile page). Password will be stored salted and encrypted, but don't forget to pick different ones for different sites. All personal informations that we store will only be used to our purpose and not selled anytime, ie not now neither ever."
Make clear your site is a side project, a beta, an alpha; that bugs may occur; that is possible to create apocalypse and kill kittens (cf disclaimer of VLC beta on Android).
More, if you keep private informations only to identify users, you can tell that all informations will be deleted (and you will) when your project will be full. (beta to production deletion).