You only really need to use a branch in the canonical repository if you are
going to do non-scratch koji builds. Otherwise you could just make your
own forked repository, which git supports nicely. (You can put it on your
fedorapeople site, for example.) OTOH, sharing it centrally is a fine way
to make it easy for people to find your branches.
The convention you mentioned is one I suggested, so obviously I think it's
fine. IMHO it would be better if Fedora were to establish a standard
convention for branch names in package repos, whatever the exact naming
chosen might be. But who knows how long til that gets decided.
If Dave and/or Kyle think {fN/,}user/<yourname>/* is a good idea too,
then go for it.
Thanks,
Roland