Optimized .htaccess file

I'm looking for an Apache expert - to make an optimized .htaccess file. The file needs to be fast, with low impact on server, and with SEO in mind. It will need to do the following... * Redirect all non-www ([login to view URL]) requests to the [login to view URL] - using 301 redirects (If 301 is best for seo) * Add a "/" forward slash to all requests to directories - but NOT to files. ([login to view URL] and [login to view URL]). This needs to work with the rule above - so if a user enters - [login to view URL] - the page needs to be directed to [login to view URL] * Set the custom error page ErrorDocument 404 /[login to view URL] * Disallow viewing of folders without index file * All sub domains must work. e.g - [login to view URL] -- the trailing/forward slash rule must also apply to subdomains. But not the www rule. E.g - a user enters [login to view URL] - the page needs to be directed to [login to view URL] * RewriteBase / must be set * Be commented so i understand what each line is doing! :-) Thanks for reading - I hope someone can create this htaccess file.