Do I have to post the story strictly here, or can I link it to fanfiction.net where my story already exists while using my comic vine post as a comment/feedback section?
Sorry for the delay. I won't say it is against the rules to advertise stuff on other sites (there are other sites???). However, I should give you the disclaimer that I don't know how well received it would be (by which I mean how many actual comments/how much feedback you would get). You could try it, but in my experience it does not go over all that well. (you could post a link in the Fan-Fic "Advertising / Help Request" Thread and you might hook a few reviewers that way. That might be best).
But I would encourage you to post it here. With this site's history of spambots, people often times stay away from the threads with off site links (even if they are from valid sources).