How far towards my ideal site can I get using available modules. And what would I need to code myself?

I've installed the minimal configuration of Drupal 7 with sqlite3 as its database. Now I am wondering how far I can get towards my "ideal site" with already made modules. I'm a programmer and willing to contribute to the community and create modules for what I need, but if there are already nice ones out there I'd like to use those and not re-invent the wheel. What I want is:

1. A multi-lingual site with two languages, English and Swedish. For this I need:
   1. A way to publish a single post in English and/or Swedish. And being able to set the nice URL for the versions to what I want (like a.com/hej and a.com/hello for the same post in its Swedish and English version).
   2. If the users browser is set to Swedish and he visits the English version of an article available in Swedish; then a small red box is visible at the top of the article alerting the user that there is a version of this article in his preferred language.
   3. Two language versions of the navigation where:
      1. Swedish (version of) posts and English only posts are shown in the Swedish version (since most people in Swedish are able to read English anyway).
      2. English (version of) posts and English only posts are shown in the English version.
      3. A way to publish three RSS or Atom-feeds:
         1. One per language version of the navigation (see开发者_JAVA技巧 above).
         2. One additional with Swedish only posts.
2. An edited post can be marked to occur on the front page again. I will mark it if I add a tip to my "Linux tips" post for example.
3. People can authenticate themselfs when commenting using:
   1. OpenID
   2. Facebook
4. I can write my posts using Markdown.
5. My code examples gets syntax highlighted.
6. The site validates as XHTML 1.0 Strict and CSS 2.1.

What can I use that is already available?

And what do I need to contribute myself?

Are there any relevant modules I should look at extending for what I contribute?