The 404 may be caused by a space char in “thank-you page”
Browser may request thank-you%20page or thank-you+page
1) Yes. You just need to change a template file index.php (and sometimes archive.php)
* Go to the theme editor
* Select the file index.php to edit
* Remove <?php the_content(‘Read more »’); ?> from the template.
If the file archive.php exist do the same operation with it.
2) No it’s not okey for seo from the SE perspective.
good luck
