Some advice:
1. Very few people care about a "free and open-source social network built with and steered by the community". You can't build a social network for just those people. It'll feel empty, and they'll leave. You need to attract lots of people who don't care about that.
2. Get rid of your landing page. See #1 for the reason. When people land on your domain they should be prompted to sign up, or look around. That's what a social network is for, after all.
3. Focus on making it work. Get to a MVP. Quietly open it to the public. Call it a beta. Don't waste time on press releases.
4. If you can't make it work, make it look like it works. No one wants to join a social media site that isn't working. "Eh, I'll join in a few months" and they'll never come back again.
5. Stay true to your principles! But keep it classy! Remember when websites would have a little "fork me on github" button in the upper-right corner? That served as a subtle indication that the project was open. That's all you need to capture the group of people I mentioned in #1. Here: https://github.com/tholman/github-corners