In a few hours I will launch my first open source startup. Any advice?

Try and get your open source community to support your launch. Although there's anecdotal evidence that having too many new accounts voting for you can get your launch banned. Good luck with your launch Grzegorz!

Push the announcement across all your social media sharing the link to your launch, and push it hard. Ask for feedback, honest feedback. Use imagery (launching now, etc.) it helps gain attention quicker. And lastly, DM people directly, best way of getting people to sign up. Hope it goes well, and best of luck!

Try to get people on twitter to share it

To use Modeliks for afterwards financial planning and pitching :) FYI we are lauynching today :)