Need Help Setting Up URL/Permalink Structure

I’ve read about a lot of things that are close to what I’m looking to do, but for some reason they aren’t working or I’m attempting them incorrectly.

Right now I’m working on using a WordPress 3.1.3 installation as a CMS for my entire website, not just my blog. So what I would like is for the blog front page, single blog posts, category lists, and tag lists to all have a starting URL that looks like this: http://www.mydomain.com/blog/

So far I have it working for the blog front page and category links. However, tag pages still show up as http://www.mydomain.com/tag/tag-name, and single blog pages bring back a 404 error when I try to visit them.

Currently, I’m using the following line in my .htaccess file, as per one of the threads I found to get rid of the category link:

RewriteRule ^category/(.+)$ http://www.mydomain.com/$1 [R=301,L]

I’m also using a custom permalink structures that looks like this:
/%category%/%postname%

Category Base: blog
Tag Base: blank/default (if I set this to “blog” I get 404 errors on the tag pages)

Hopefully all of that makes sense. I would appreciate any information you can give me. I’ll be checking this thread regularly as this is one of the last things I’m stuck on with this project. So if you need more information, feel free to ask and I should get back to you quickly.

**EDIT**
Some more information I had forgotten about.

With my category structure, I had all of my categories as a child to a category named “Blog.” That’s what gave me the correct URL structure for the single post pages, but also what was causing the 404 error. So I’m back to square one with the single post pages again.