Programmatically set page_on_front

get_page_by_title() returns an object.

Use $homepage->ID.

You should also check if you really got a usable return value:

$homepage = get_page_by_title( 'Front Page' );

if ( $homepage )
{
    update_option( 'page_on_front', $homepage->ID );
    update_option( 'show_on_front', 'page' );
}