Rewrite rules for pages that do not exist in the database - apache

Question

As of now, my htaccess looks like this
RewriteEngine On
RewriteCond %{QUERY_STRING} ArticleID=([^&]+)
RewriteRule ^article.cfm$ /articles.php?id=%1 [R=301,L]
RewriteRule ^([a-zA-Z0-9-]+)$ page.php?slug=$1
RewriteRule ^([a-zA-Z0-9-]+)/$ page.php?slug=$1
ErrorDocument 404 "<H1>Page not found</H1>"
The first 3 lines allow me to redirect users who are access articles through .cfm to .php instead
For the 4th and 5th lines, my website allows creation of pages through a WYSIWYG editor and allow users to access it. The actual url will look like www.website.com/page.php?slug=homepage but after the rewrite rule, it will look like www.website.com/homepage
However, I was having problems where my admin pages such as www.website.com/admin/ was regarded as one of the page so I added the below codes and it works
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule .* - [L]
But I'm still having a couple of problems.
If you access an invalid page such as www.website.com/hello/ when there is no such page created by the users at all, it will still show page.php but with empty contents, how do i redirect it to a 404 page?
How do I secure directories which does not have an index.php page? such as my images folder, includes folder, javascript folders etc?
Does my entire htaccess looks right at this current point?
Thank you guys so much for helping! I'm not good with mod_rewrite so I will appreciate your help!

Answer 1

If you access an invalid page such as www.website.com/hello/ when
there is no such page created by the users at all, it will still show
page.php but with empty contents, how do i redirect it to a 404 page?
You should do this with PHP. If there's no content included, use header() to redirect to a 404.
How do I secure directories which does not have an index.php page?
such as my images folder, includes folder, javascript folders etc?
Add this to your .htaccess: Options -Indexes
Does my entire htaccess looks right at this current point?
Looks fine.