Blizz stated in a watercooler that they're using the 1.12 database as a starting point. I don't think it's a stretch for people to assume that most game features and mechanics will be in their 1.12 state. The kind of stuff I would expect to see reverted would be numerous AV changes, but I seriously doubt class mechanics are going to be reverted. I'd be surprised if the threat changes that ruin pre-naxx encounters are reverted.

Affliction: Endless Affliction - Your Unstable Affliction deals the same damage as normal, but its duration is increased by 6 sec. Demonology: Nether Ward - Surrounds the caster with a shield that lasts 3 sec, reflecting all harmful spells cast on you. Destruction: Demon Armor - Protects the caster, increasing maximum health by 10% and increases armor by 150%. Warrior
In terms of what the World of Warcraft Classic Best Classes are, Warrior and Priest stand out almost instantly. This is partly due to the fact that Protection Warrior is the only viable Tank Class in WoW Vanilla Patch 1.12. Both the Proc Warrior and Priest are required for Raids and when combined in a PVP setting can be a fierce combo on the battlegrounds.
The quickest way to level up is to travel through the game's zones, completing all the quests you encounter along the way. Completing quests grants you Experience points, which will slowly fill in your experience bar with blue or purple. When the bar fills, you reach the next level. Alternatively, you could choose to run Dungeons or Battlegrounds, which are not covered in this beginner's guide.
And for talent builds. I prefer to make my own talent builds. But I've been playing RPGs since the 8bit days so half the fun is building my own characters up. I already made and bookmarked 1 deep fire mage build, 2 elemental mage builds, and 2 deep frost mage builds. And I might remake them tomorrow if I read up on any good talent choices I left out my 1st 5 times lol. And I have multiple builds for the other classes I play too.
 ":"  -  Any time a step ends in a ":" instead of a "." means that the next step is part of the current step you are on.  This generally means the next step should be done while working on the current step.  This means every "start working on" or "continue working on" will end in a ":".  But this is used with other occasions as well, so keep this in mind.
ConsolePort: A WoW addon which natively supports Xbox and DualShock controllers. WoWMapper: Third-party software for keyboard and mouse emulation. This software is not against the ToS, because it does not automate your gameplay. Multiboxers are without any issues using ISBoxer for instance. Xbox or a DualShock controller: Alternatively, you can use a Steam controller and enable Stream streaming. Setup instructions can be found here. DualShock's touchpad acts like a mouse, which is quite nice. A long HDMI cable: In case you decide to hook up your PC to a TV. Instructions