Do I need a Launchpad project to push a branch?

For any software product it makes sense to invite collaboration by providing a framework around which people can work. Launchpad provides this framework in terms of a project, which is registered using https://launchpad.net/projects/+new-guided

However, for quick tests and initial sketches of software, creating a project can mean a bit of overhead and might invite premature commentary. You can rely on non-project branches (sometimes called +junk branches -- because if it's not shared, it's probably junk!) for that purpose. Read more about +junk branches at https://help.launchpad.net/NonProjectBranches