Hi @Idealien
I see 2 issues with your above code:
1. Your post_meta function use the $post->ID, however your get_field does not
2. Your setup_postdata() function may be causing the issue.
Does your line work correctly:
$output .= "<strong>ID: " . $post->ID . "</strong><br/><br/>";
Can you also read over the WP docs to see some code examples of loops. Perhaps the get_posts function will be clearner?
Thanks
E