tangor has some good points.
I'm wondering however, if you are asking the right questions. Pinging and submitting RSS feeds are post blog creation issues. If you are just setting them up, of course add the option of the RSS on your site, but mostly I would focus on the data generation and kw targeting.
I would stick to wordpress compared to livejournal (more verifiability).
There are mostly time investment concerns; I have worked on in the past-most of my sites have benefited exponentially due to pre planning and focus, and then offsite promotion.
1. Get your blog plan in place
2. Develop 20-30 quality SEO/shareable posts
3. Get 5-10 authority guest posts (spaced out within your posts)
4. Add/start submitting your content (in this case later is better than sooner, as your quality will be more easily verified).
5. feedburner only helps sites that will generate longterm traffic, and will probably be less relevant in the next few years, so don't make it the focus of your efforts.