Disable Network / Migrate WPMU to Single Install

I am trying to take my multi-site wp install and disable the network so it is only the single install on the primary site. I migrated our old buddypress forums to bbpress (successfully), disabled all network active plugins, deleted all the ones we didn’t neeed including bp, and re-activated updated versions of all the plugins on just the primary blog. At this point, everything was cool.

Then I followed the instructions on this link https://premium.wpmudev.org/blog/how-to-uninstall-wordpress-multisite/ to the letter. This includes editing wp-config by deleting the following:

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
$base = '/wordpress/';
define( 'DOMAIN_CURRENT_SITE', 'localhost' );
define( 'PATH_CURRENT_SITE', '/wordpress/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );

and changing this line from true to false:

define(‘WP_ALLOW_MULTISITE’, false);

and then editing the following in htaccess so it reads as:

RewriteEngine On
RewriteBase /wordpress/
RewriteRule ^index.php$ - [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*.php)$ $2 [L]
RewriteRule . index.php [L]

And then I dropped the spam and delete columns from the wp_users table and removed the following:

wp_blogs
wp_blog_versions
wp_registration_log
wp_signups
wp_site
wp_sitemeta

This left me with a 500 internal server error.

Any ideas on where I should start hunting down the problem?