Trying to move from live to local server, but getting a "500 Internal Server Error"

So I'm trying to do the reverse of this video and copy a client's live site onto my local server in order to test a new plugin. However, when I try to navigate to the page in Chrome, I get a blank page, and Developer Tools shows a 500 error.

Here is what I've already done (in order):

1) Exported MySQL database as a zip file, and imported it into a database with the same name on my local server

2) FTP'd the entire Wordpress directory to MAMP's root folder (with the exception of two folders consisting of only audio content, because they total about 8 GB, but I don't think that should matter...)

3) Used SQL to update links in the wp_options, wp_posts, and wp_postmeta tables to point to the local server

4) Updated wp-config.php and set DB_HOST to "localhost", DB_USER to "root", and DB_PASSWORD to "root". Also added defines for WP_HOME and WP_SITEURL and set them to http://localhost/my-folder-name

I'm not sure what to try because I'm pretty new to this. What am I missing? I appreciate any help!