How to make a custom page in Wordpress

Hi I'd like to create a totally custom page in wordpress where I'd add a lot of php code so I would prefer not to create it as a wordpress 'Page', but as a file 'filename.php' in my theme directory. Of course in that page I need to include wp functions and stuff and I plan to do it with require_once("../../../../wp-load.php");.

My problem is, how do I set the header info for a custom page like that (title, meta description etc..) and how do I add a rewrite rule to make it reachable like "website.dom/pagename". Thanks in advance for any answer, and even if you tell me that the best way is to use wordpress default "Add New Page", I'd prefer not to use any script to insert php code in the page, thanks.

via Chebli Mohamed