I know that it is important to have an error document for 404, 403, 401 and 500. But what others, if any should I make to be completely sure that users do not see the default apache error page?
I suggest that you use a custom error page at least for the 404 and 410 code.
Providing custom error pages, makes your website look more professional and more live, also it reduces the possibility that the visitor will bounce.
Specially on websites where content is regularly deleted (eg news sites, advertisements sites, aggregators etc), it could make a difference.
Also custom error pages are useful, to handle wrong hits - links. For example it is possible that people that want to link to content to your website, or share links using eg email, will not use the correct url, but for some reason the url will be a little different. This could be due to a wrong copy paste.
For example you have a post www.example.com/how-to-tune-nginx-with-php-fpm, and the link will be www.example.com/how-to-tune-nginx-with-php-fp
In this example, the person that copied the url, forgot to highlight the last character [m] of the url.
Now think a website where you have a post, and for some reason you delete it. This post could be indexed by search engines or be linked by other websites.
If you are not providing a custom 404 page, but displaying the apache's default, it is sure that the visitor will bounce. But if you are displaying a custom 404 with some links similar to the post that the visitor tried to open, it is possible that he will click some of these links, and you will get an extra pageview
Eg: You search on google: "How to boost my seo", you click on a result, but the result is no longer available. If you see the default 404 error page, you will bounce.
But if you see a custom page with some more options, you could stay a little longer on the website. For example you could have a page like this:
This page is not longer available. Instead you could see: - Top 10 tips to improve SEO - Techniques to boost rankings
To my opinion, custom 404 and 410 pages are very helpful. I have tested and seen that visitors are clicking the provided links found on a 404 error page, and stay longer on the site :)
PS: Stackexchange do use custom error pages. Try to go to a url that does not exist. For example on this question change the url from 58470 to 60000 (questions/60000/should-i-make-a-page-for-every-http-error)
A custom error page will be shown.
Or remove some characters from the url, and you will see that stackoverflow fixes the url with a redirection