Before you start

Hello Everyone.

I am trying to determine if Drupal CMS can be used as a back end admin tool for a already existing Ecommerce website built with the following tech stack.

Java/J2EE
HTML/CSS Javascript.
MySQL database
JBOSS app server

Ok, so I am a brand spanking new member (so please don't flame me!).

I have just finished creating the following website: http://www.atlasofpaducah.com.
I have a test domain here: http://testing.atlasofpaducah.com for new features and such.
I have installed drupal 6 here: http://testing.atlasofpaducah.com/drupal/.

So, I like my site and the custom silverlight apps that make up the flashier features of it, BUT...it's just missing one thing.

News content management.

So, a few google searches later and some drupal reviews, here I am :)

Things to know: I like the way my site looks and works (custom navigation with silverlight app, custom slideshow viewer in silverlight, and custom brands viewer displayed in, you guessed it, silverlight).

So, i'd like to know if i can simply use drupal as the administrative backend (see the above link) and "plug" the content into my site where i want it.

I.e. administrative users go to the drupal part of the site to update the latest news story, and poof, it appears in a news section under my navigation menu. Same thing for the home page's content.

Is there a way to plug in drupal output into an existing site, or do I have to retemplate the drupal site just to use drupal's functionality (not desired, the website is more of an informational brochure, and therefore doesn't need logins for customers, forums, etc.).

I want to make a site that would link with Facebook fanpage, twitter account and youtube accout for videos.
I want to have any news updates on my site be reflected on Facebook or twitter.

I am also interested if it is possible to upload a video on your site and have it uploaded automatically on youtube channel (is it possible with some kind of module?)

I also want some users to be able to upload their own photos or videos (only in some section of my site).

I am new to Drupal & also to CMS world. So would really appreciate if someone can guide me & provide some clarification to me.

Requriement:
I want to host more then one site on same physical server & both these sites will have separte domain/url. Can I acheive this using Drupal or any other CMS (if not Drupal)?

I also wanted to understand the steps involved (at high level) from creation to hosting of a site created using Drupal. Assuming that I will use a dedicated server with some data centre & will do installation on my own.

Are there any modules to fill in a two-dimensional tables (rows and columns) through the user interface?

Would it be possible to create a groupon.com like site for a niche community using drupal? I am assuming I would could use Ubercart module for the check out part.

Thanks!