Custom Query: query by post custom meta data

Since you’re using WP_Query(), you should consult the Codex entry for WP_QUery(). It lists all of the parameters that can be passed to the arguments array.

In this case, you want to use the post custom meta parameters.

Assuming your custom meta key is _show_on_front, and your value is true or false:

<?php
$custom_query_args = array(
    'post_type' => 'Event',
    'posts_per_page' => 1000
    // INSERT POST CUSTOM META PARAMETERS HERE
    'meta_key' => '_show_on_front',
    'meta_value' => true
);
$custom_query = new WP_Query( $custom_query_args );
?>

For more complex examples, consult the linked Codex entry.