Heavensward must be installed on the client to access the areas that will be added in Heavensward. If you are planning to log back in on a client that doesn't have Heavensward installed, make sure to log out in an FFXIV: ARR area.

This interests me most. It doesn't say you necessarily have to have BOUGHT it, just that you need to have it installed.

This mgiht be where torrents or friends with the other version of the game come in handy. I'll bet that you can buy the PS4 version, and just install the PC version and your Service Account should have access to all the patch areas. (Basically using the code from the PS4 version to make yours a 'Blue skies of Ishgard' account.)