Moving wordpress core files to new directory, blog stays in root

I have a wordpress installation in my root directory of my domain, with
wordpress core files in /wp/ folder. I want to keep my blog in the root
directory, but have the wordpress core files in a new folder /new_wp/.

I backed up database and all files. Then I made the new folder /new_wp/
I copied into the /new_wp/ folder the core wordpress files which
I got fresh from download. Then I uploaded the /themes, /plugins/,
etc folders from the /wp/ folder to the /new_wp/ folder.

Next, I edited the index.php file in the root directory, to point to
the /new_wp/ directory. Then I logged into my admin panel at /wp/ and
set my site url to /new_wp/ directory. Keeping Home how
it was for the root directory.

Now when I go to the new admin page https://mysite.com/new_wp/wp-admin
I get the login screen, can login, and then only a blank page displays. There is no dashboard / admin area. I cannot log into the old /wp/ admin site. (I do know how to change the siteurl setting back in phpMyAdmin, by edit in wp_options directly, to get back into /wp/ admin site IF I need to do that).

My website itself still comes up, but there are some features missing on it.

What did I miss?

1. I presume after I changed the siteurl in the admin panel,
then I need to download the /themes, /plugins, etc (whatever files changed) and move those updated files to the new location?

2. Perhaps there are some entries in the database that need to be changed to the new siteurl?

????