I’m not sure what the root cause of your issue is. But I do see a syntax error in your last code block, which could be what’s causing the white screen. Your “action” attribute is missing a close quote. Try this instead:
<form action="<?php echo esc_url( admin_url('admin-post.php') ); ?>" id="new_post" name="new_post" class="form-horizontal" method="post" enctype="multipart/form-data">