In answer to your questions:
1) The demo site includes all features built into the theme and does not include any plugins or extras, so yes, that is what you get when you buy the theme (apart from demo listings and categories of course) ;)
2) In order to allow both free and paid for listings, you would create "plans" for the various types, related to categories. In the plan settings, you can determine the price and duration of a listing, as well as whether or not the listing is featured. You can see this specific page in the
Vantage admin demo. If you want to charge for listings (whether or not you have free options), then you would select "Yes" to charge for listings as this will allow the payment gateway step of the process.
3) The payment option is in the last step of the listing process.
4) Changing the text of the button would require some minor modification to the default theme code.
5) Featured listings appear in the order by which they were posted. Essentially if someone pays to relist a listing then it should appear as a new listing.
6) Moderation can still be in place even if a listing has been paid for, by that time though, yes the customer will have already paid for the listing.
7) Vantage is not currently responsive, however this is a planned change for version 1.2 of Vantage, with the estimated release date indicated on our
theme release status page. Thanks.