To be honest I think it's a bit too early to say right now. On the PTR even in heroics tanks are getting beaten up pretty hard, as they scaled up monster damage output, so the numbers will probably get rebalanced a bit before the patch goes live.
The biggest thing to get your head around right now is the revamped system of every healer having the three base heals - the slow, small efficient heal, the slow large heal, and the fast inefficient heal. They apparently expect healers to use the slow small heal when there is not much else to do, and to balance the other heals with their cooldowns during heavier damage.
Also, right now I'd pay more attention to what Blizzard says about healing than what the experience is like on the PTR. Here are some recent examples:
The reason I say to watch what they say more than what they do is, they've been very clear that if the PTR behavior doesn't match what they have in mind, they'll tweak the numbers until it does. In the last PTR patch most healers just spammed their slow, efficient spell because it was getting the job done... so in the next patch Blizzard nerfed those spells, as they want them to be only a fallback and not strong enough to stand alone. That sort of thing may well happen once or twice more before the patch goes live.
Incidentally, I find that checking the top page of mmo-champion to be the easiest way to keep track of Blizzard's position on things.
You cannot play the original World of Warcraft as Cataclysm changed the map, starting areas, and other things significantly.
To clarify, this does not require you to buy any of the expansions, but it does require you to patch your game so that you're on the current version of the game. Even without buying the expansions there are many changes that will effect how you experience the game.
Best Answer
When available, the Portuguese Language Pack will likely be on this download page. The one for Spanish is already there, so it's likely that Portuguese will be there as well.
You may also want to keep an eye on the WoW Brazil FAQ page, as that's likely to have information relevant to your question as it is available.