Hi,
about error 404 --> some facts:
1) for users it's unnecessary page, they want working page withouts any "strange" errors. So make sure that you don't have it - every month, there are few tools to check it. So if users will see home page, they say okey ... there wasn't any page that I was searching for. But if he will see Error404 - upss.. they have broken page or I have made mistake ?
2) Our template - like any others templates uses standard error page functionality (gk_TemplateName\error.php) - with just have a little bit different appearance.
3) Template should not be response for generating 404 errors - Joomla does. You can check it - changing a template to default.
4) For capturing errors you can use different component for example: Qlue Custom 404 (Free/Pro)- he will use article where you can put some info, links and funny picture.