1. In my XAMPP which is the latest version, rewrite module is ON for loading by default in httpd.conf.
2. In my case, RewriteBase in .htaccess and .htaccess itself is not needed since it doesn't change anything. MODx setup starts successfully with and without it. I just noticed that when I set RewriteBase incorrectly - without slash in front of the subdirectory name it generates server error 500. It just proves that localhost url is working fine.
3. I can run setup until the point where I need to enter database details. The page called "Connection Information". When I enter already created DB details and already created user details and click on "Test database server connection and view collations." and get this error:
Connecting to database server:
Could not connect to the database server. Check the connection properties and try again.
[2017-05-13 14:01:43] (ERROR in xPDOConnection::connect @ C:\xampp\htdocs\mywebsite\core\xpdo\xpdo.class.php : 3116) SQLSTATE[HY000] [1045] Access denied for user 'dbuser'@'localhost' (using password: YES)
[2017-05-13 14:01:43] (ERROR in xPDOConnection::connect @ C:\xampp\htdocs\mywebsite\core\xpdo\xpdo.class.php : 3116) SQLSTATE[HY000] [1045] Access denied for user 'dbuser'@'localhost' (using password: YES)
Sometimes instead of this error I get charset related error message.
At this point no core/cache/logs generated yet - no such directory or file.
I tried first to allow modx to create DB and user but it didn't work so I create it manually via phpMyAdmin.