Specifically what are your questions, let's see
(1) Categories
At wordpress.com Categories and Tags are the same thing. Technorati spiders pick up all categories without any difficulties.
(2) Blog promotion
If you want to be sure you've covered the bases when it comes to blog promotion then this is a helpful link http://faq.wordpress.com/2006/11/15/more-traffic/
We also have many threads in the forum search box on increasing traffic to your blog. From time to time we start another one and simply reiterate everything that's been said before.
In a nutshell:
(1) Promoting your wordpress.com blog will be more effective if you edit your profile and link your wordpress.com username to your wordpress.com blog.
(2) Promoting your wordpress.com blog will be more effective if you regularly post high quality, original content posts to your blog.
(3) Promoting your wordpress.com blog will be more effective if you tag your posts with categories that are specific to your blogging topics.
(4) Promoting your wordpress.com blog will be more effective if you invest time and energy into leaving meaningful comments on other blogs, in forums and on websites related to your blogging topics.