Can there be something similar to a wildcard directive to trap all possible errors and cope with these questions single custom error page?

ErrorDocument 404 /error.php?code=404
ErrorDocument 403 /error.php?code=403
...
ErrorDocument NNN /error.php?code=NNN #possible use of RegExp?

I understand I most likely will not be dealing with many different custom error pages here, but I am interested in this.

That's difficult. You must have a ErrorDocument directive for every status code you need to handle in a different way compared to the default error handler.

Instead of passing within the error status code, you are able to get it inside your script through the REDIRECT_STATUS atmosphere variable (set by Apache). See: http://httpd.apache.org/docs/2.0/custom-error.html