Hey Andrew,
I would suggest having a category regarding small business and news within your blog, yes... I would also suggest having a category for your product, discussing a feature per post loosely marketing it to your visitors. Have a section to discuss new features you are working on (if you are happy to do so), also request feedback about other features are of interest. Ideally you want a few different sections, this will offer you a number of ideas to write posts on, but also it will diversify your content.
As for "taking great content from elsewhere on the internet and adding it to my blog" I highly recommend against it. However, you can re-write the content (perhaps, combine the details of more than one post).
Duplicate content is a world of hurt you don't want...
Cheers,
Dan
PS> If your question is answered by any of the great responses above I urge you to mark it as 'Answered'. You can mark more the one response.