Nice site design. Looks great.
It seems you need to build a custom WordPress theme rather than find plugins. Grab a blank theme like Toolbox by Automattic http://wordpress.org/extend/themes/toolbox and put your CSS skills to work. Most theme skinning can be done with CSS.
You will also need to learn how to cut and paste and rearrange PHP a. You can find good references if you search (upper right) the codex here http://codex.wordpress.org/.
For searching for plugins, search here http://wordpress.org/extend/plugins/, or you just can't beat Google. You can't always find a plugin that does exactly what you want. Sometimes you need to customize.
Announcement at the top: I don't know of a plugin to do this. Find a jQuery example and copy it.
Content scroller: There are many slideshow plugins. Try Googling: "wordpress plugin jquery slider" or "wordpress plugin content slider". If you can't find what you want, you might need to manually customize a jQuery slideshow.
Custom modules: You could try the plugin http://wordpress.org/extend/plugins/multiple-content-blocks/, or add custom fields to your home page, or better yet create a custom post type http://codex.wordpress.org/Post_Types and display them on the home page.
Latest post on the blog: You could go to admin > Settings > Reading > Blog pages show at most: 1, but that would also show only 1 post on a blog page if you have one. Alternately you could add before the loop in your index.php:
query_posts('showposts=4'). Google is your friend, try "wordpress change number of posts on front page".
Display lists of grouped pages: In WP admin, create parent/child relationships with pages, then add some code to your theme from here: http://codex.wordpress.org/Function_Reference/wp_list_pages#List_Sub-Pages.
Good luck! WordPress makes a good CMS, and is very friendly to designers.