I wouldnt consider it "black hat" as long as you're providing valuable, rich content, that is agnostic to your brand.  If you have any other companies in your industry that could also add content, you could really gain some traction and use it as a marketing tool for the industry with some leverage toward your brand.

That being said, there are much more qualified people who could probably clarify issues.. these are just my guestimates.

Now, the same IP address could create an issue.. you may want to host it on another server.

I would keep and _tags for specific keywords, sentences, quotes, etc. However, if it is for purely cosmetic reasons your editor wants to bold the first sentences, it should be an easy CSS hack that will help the visual aspects of the content be seen.  _

Remember to incorporate best practices into all your code and remember how the content is being crawled.

if you can get both twitter accounts, why not take them both and sit on the keyword twitter. It may be valuable in the future for industry leadership, etc.  But for marketing and branding definitely go with your company name

Agree with William. WP is pretty much king of the castle right now in terms of CMS.  I also recommend taking a look at joomla and drupal.  I personally love WP and recommend it to everyone, but some projects really do require different strengths.  I'm also a big fan of opensource.