Sem-La

Tried to download and activate WP Clone today. Got a fatal error message as well, but not on an empty wordpress installation. Upon reading the error message, it was connected to a plug in. My solution: deactivate the plugin causing the error, activate WP Clone and it activated without error.

You can change the background picture in the customize section.
Go to your dashboard, appearance, customise, scroll down to background image, do what you want to do there and click on the save and publish button on top op the customisation bar.

Good luck!