1) I think you are better off to have one installation of WP and GD at the main domain name. That way your visitors can search more than one neighborhood at the time, the listing they are looking for might be just across the boundary. The way you propose would mean that a visitor who wants to review a few listings, or a user who wants to add his different businesses across different neighborhoods would have to go through the registration process twice, and will need to log in to more than one site when coming back later.
If you really wanted to have different sites for each location, you are best to set up a multisite, with each location in a subdirectory. At least users will be shared across the sites then, but they still will not be able to search across the different sites then.
2) See #1.
3) The payments and prices manager allows you to create different packages with different privileges. For example a free package with only one image that can be added to one category, and a paid package with max 20 images, can be added to 5 categories, can add facebook link, and is featured on all pages where it is shown.
4) If you use PayPal or Stripe, you can set up price packages that are automatically charging every month or year etc.