Technical Specification

I've followed this group for awhile, because I have created a lot of business directories outside of Drupal, and have wondered if it could be done easier and quicker within Drupal and it's vast amount of contrib modules. Well, I think it can, now that I do 90% of website development work in Drupal.

I am trying to create a system like http://atlanta.craigslist.org/, where users can post anything they are selling. This is what I did so far.

1) I created a content type called "marketplace listing". I used CCK to add various fields.
2) I created a container vocabulary called "Marketplace". Then I added terms (categories) in a tree like structure. For example, see below:
Marketplace
-For Sale
--Books
--Electronics
--Clothes
--Computers
-Jobs
--Accounting
--Finance
--Engineering
-Housing
--Apartments
--Condos

I am new to Drupal. I have watched many tutorials on how to use Drupal, but I have no idea where to start for this project.

I am almost done with the development of a social business directory, and would love to start the SEO side of things, in which I am not well versed at.

The website structure is divided into 3 sections: Business Directory | Events | Community

Business Directory content is added by the following node types:

1. Entertainment
2. Health
3. Religious
4. Restaurant
5. Service
6. Shop
7. Website

Events content:

1. Event

Community Content:

1. group
2. group post
3. album (photos)
4. question (answers)
5. blogs

While setting up a business directory, I would like each business listing to be able to maintain a buddylist/fan base. SO for example if a business maintainer has new stock, they can simply email all the business fans/buddies.

Now the problem is should I let "businesses" be "groups", with a custom group/business page, so users can join(become fans) of a business, thereby automatically being able to opt in/out of mailing lists.

Or

Should I create a CCK node-type and use usernode to make use of the buddylist module. (not sure how this works though)

thanks