If you post an article on HN that has text instead of a link (that's the two options you've got, read the 'submit' page, it literally says "Leave url blank to submit a question for discussion. If there is no url, the text (if any) will appear at the top of the comments page. If there is a url, the text will be ignored.") then your post will be ranked differently from the posts that contain just a link to a URL pointing elsewhere.

The 'self' presumably refers to the article being HN only.

To avoid meta-discussion and 'Ask HN' style posts clogging up the new page they are penalized, so they'll typically drop off faster even if they do receive a lot of votes. And if they don't receive a lot of votes then they're gone even faster.

So if you want your 'rate my startup' post to be seen best just post the link, and add any extra info as the first comment in the thread.