Having taken a step back from migrating this blog over to D8 by waiting for the full release of D8.0.0, time has pushed on!
Starting a D8 project today is a different beast entirely. Rather than download a tar ball and manually installing, it's possible (and nay advised!) to use composer to install. The best project for this currently seems to be https://github.com/drupal-composer/drupal-project
To start from scratch with a blank project using drupal-project:
composer create-project drupal-composer/drupal-project:8.x-dev some-dir --stability dev --no-interaction