There is no notification system in place. People will read a story because it is on the first page. Bear in mind we have over 150,000 members currently, and even more 'guests' on site every day, so people who will go into a section of the archive periodically just to see what's new will often click on stories updated since their last run through.
There is currently no way to see how many 'subscribers' your story has - in this case, I'm interpreting that to mean how many people have added it to their favorites list.
You may certainly post in the promote a story forum, provided that the story is hosted here on AFF. The rules and regulations of that forum are found here.
No, you may not use your review board as a communications tool. That is expressly forbidden in the Guidelines, which are part of the Terms of Service of the site:
What we recommend is to create a thread in the appropriate sub-forum here in order to reply to reviewers as well as make any author's notes that exceed the 600 word limit. Users do not have to be members of the forum in order to reply to your threads there, and what you would do is, once the thread is created, copy the URL into your story chapter (either at the top or the bottom) to let readers know that you will be replying to reviews there.
(Example from one of mine:
"Review replies can be found here: http://www2.adult-fanfiction.org/forum/index.php/topic/52114-review-replies-alternative-learning/ ")
The URL will show in full within the chapter of the story.
I hope that answers all of your questions, and we'd certainly prefer that users ask if something is unclear to them.