Don't use Homebrew. I am generally a huge fan of package managers, and Homebrew is pretty much my jam. However, using it to install Postgres turned out to be a major headache. I'm fairly confident it works, eventually, but time was not feeling generous in regard to letting me test that hypothesis.
Use postgres.app, which not only is way easier to install, but also gives you an adorable elephant icon in your tray.
psqlcomand available in terminal by adding
PATH="$PATH:/Applications/Postgres.app/Contents/Versions/9.3/bin"to your bash_profile.
You can now launch Postgres just as you would a normal app and you'll be up and running. Voila.