Each topic is a completely new post. Dependent on the volume of news you should distribute, you can create new topics daily or several within 24 hours. Don't give away too much information in your site content. Enticing text should prompt readers to click right through to your main site, when the action (and point of sale) is. Use keyword rich text entice those spiders that mine data from RSS. Since your catalog grows, as you are submitting more books or approach to new projects, you could have more material for your feed.

Imagine how hard there must be to generate traffic to see just your content