[Angel-Wings]

Hello

The code looks ok so far, still instead of trying it the "htaccess" way you can also do it directly in your Webserver:

<VirtualHost www.example.com>
ErrorDocument 404 /index.php
ErrorDocument 500 /index.php
...
DocumentRoot /this/is/an/example/

<Directory "/this/is/an/example/">
AllowOverride None
...
</Directory>
</VirtualHost>

This would set your Error Documents directly in the configured Host without any htaccess directives.
Additionally the "AllowOverride None" directive disables "htaccess" completely - Apache is a bit faster then because the lookup for ".htaccess" isn't done.
Instead of writing .htaccess for each single directory, configure it directly in the Webserver config if possible and disable it with "AllowOverride None"

http://httpd.apache.org/docs/2.2/misc/perf-tuning.html

Explains the reasons