Currently our practice (not very reliably followed) is to maintain one branch and tag at release. A release tar ball should also be published. This policy was developed back when backporting livecd-tools to older releases pretty much wasn't done.
We seem to be moving toward pushing back new releases into older Fedoras. If we have some significant user impact changes (of the need to change workflow kind), we may end wanting to track separate branches. Also even adding feature changes mixed with bug fixes may cause us to run afoul of the updates policy. So we should at least be thinking about what we would want to do for branching, even if we don't need this right now.
Given the lack of manpower we have, and that our new features don't tend to break users' workflows, I would be inclined to just have one branch for now and tag when making a release tar ball. If we get push back on doing updates in Fedora, then I think we will want to start using branches for bug fixes. (The alternative is to use patch files in the packages, but that gets messy and is more work.)