Your subscription is technically for Modern World of Warcraft, with an active WoW account you get access to the various other versions, like Classic Era, Burning Crusade Classic Anniversary, Mist of Pandaria Classic and upon launch, World of Warcraft Forever.
Any subscription option will work for that. 1 month, 3, 6, or 12 or even the game time that comes from a WoW Token purchased for gold in Modern WoW.
As for the other mounts and pets, if it doesn’t specifically say World of Warcraft: Forever, it is unlikely that it will be available in that version. They may eventually be updated, but Support has no insight into that. Keep an eye on the available blogs when those are updated/released.