Pin to Top Functionality using orderby custom field then event date

I had a similar aproach some days ago

//.....
'meta_query'      => array(
           'relation' => 'OR',
            array(
                'pin_clause' = array(
                'meta_key' => 'pin_to_top',
                'meta_type' => 'NUMERIC',
                'meta_value_num' => '1',
                'compare' => '='
                )
            ),
            array(
                'date_clause' => array(
                    'meta_key' => '_EventStartDate',
                    'meta_type' => 'DATETIME',
                    'meta_value' => '$today',
                    'compare' => '>='
                )
            )
        ),
        'orderby' => array(
            'pin_clause' => 'DESC',
            'date_clause' => 'ASC'
        )
 //....

I don’t know if I got your names right, but I think it will help to understand the trick.