This forum is for questions so feel free to post as often as you have them.

As for you question the only things Heavensward adds that isn't the new content for players above lvl 50 is the ability to pay Au Ra and the ability to level above 50. As a result your not losing out on anything not have Heavensward yet while playing before 50.

At 50 you will need to go through the patch story if you wish to continue onto Heavensward content. This content does not require Heavensward either. However if you have Heavensward unlocked you will get some experience from quests during this part of the game. For this reason the first time you really want to consider getting Heavensward is when you get up to 50.

Apart from that everything else, including the Gold Saucer stuff, is accessable without it.