rudolf45

If you want the best of both worlds: i.e. using WP as a “newsfeed” for your main site and having it as a blog, too (where visitors can comment etc.) then I am afraid your only choice is to make a theme that loks exactly like your existing site.
There is a lot of information in the Codex about theme building:
http://codex.wordpress.org/Theme_Development
http://codex.wordpress.org/Blog_Design_and_Layout
and ask here whenever you need more help.

WP is not an image editing tool, which means you should edit (resize) your images before uploading them.
The thumbnails are created automatically when you upload a picture using the inline uploader.
After the upload you should have an option to select what do you want to display: thumb or original size.

If you have a bbpress related question, maybe the guys over there could help: http://bbpress.org/forums/

Only the folder with the name I gave you above – it should be in (under) the “plugins” folder.

Those are abbreviations. (google for it)
If you want to change the look/behaviour – open your stylesheet (style,css) and look for

abbr {
something: here...;
}

If I remember well this plugin has an option to show posts by authro:
http://www.coffee2code.com/archives/2004/08/27/plugin-customizable-post-listings/
I guess you could set to show 1 post by X author… and then once again from the Y author.
(Maybe it’s not the optimal solution – but you could give it a try until something better is found.)

Re-installing always wipes out the old database = you’d lose your existing posts!
Check the index.php in your WP directory and replace it if necessary. Also, check the index.php of your theme.

And, of course, the usual steps: tell your host; change all your passwords, check the file permissions and never leave any file writable (like when editing theme files online…)

Did you try reading about using Permalinks? And, additionally, to visit your own admin panel: Options > Permalinks?
I’d start with those.