Yes they are, we tested it out in-game. They’re also BoE and not class specific, so you can use multiple characters to speed up your collecting process, and can buy/sell them.

Sadly not, or at least not yet. When Transmogrification was first announced, Kaivax commented with the following statement,

“We would like to offer some alternative ways to get favorite items that are no longer available…not every favorite item will be immediately available at launch. But we’ll keep a list of items that get requested by the players and work to get them in someday.”
[Source]

Numerous threads sprung up with suggestions and Tier 3 featured greatly among the requests. As such, we can’t rule out Tier 3 just yet, it may be a later addition to the feature.

Yes, Season 3 armor and weapons were re-introduced in 4.3, after more than 3 years absence. All of them can be purchased with Honor Points, from Kezzik the Striker in Area 52, Netherstorm. The head, chest and legs cost 1000 honor each, the shoulders and gloves 750.

Vindicator’s pieces still are only available by trading in Tier 6 tokens on the Isle of Quel’Danas. They’re not currently available for honor, unlike the extras from Seasons 2 & 4.

They haven’t been added back into the game yet, and there’s no evidence to suggest if and when they might return.

It was recently announced by Bashiok that level 60 PvP sets are un-transmogrifiable. Instead, replica versions of these items have been added to vendors in Area 52, which will only be transmogrifiable by characters that have obtained the feats of strength for the Legionnaire/Knight-Captain ranks and higher, from the old PvP system.

This essentially means that those who own the original sets will never be able to transmogrify them, but the appearance will be available, via the replicas, to those with the appropriate PvP ranks. The issue is rather complicated and has drawn a large amount of criticism, so this system may yet change again. Check this thread for further details.

Transmogrification will normally apply the enchant glow of your equipped weapon onto your chosen weapon appearance. The exception to this is if the source weapon, the one which is supplying the visual appearance, has a passive glow/effect on it before having been enchanted.

We’ve already found a considerable amount of items which cannot be transmogrified under the ‘silly’ or ‘absurd’ category, and there are no doubt many more which we don’t yet know about.

Among the most queried is the infamous Sandrene’s Invisible Vest (Alliance) / Sandrene’s Invisible Vest (Horde), which is, somewhat unsurprisingly, not a viable look for transmogrification. The various fish weapons are also out of the picture, no doubt to spare people the embarrassment of being double-carp slapped to death in battlegrounds.

To the disappointment of many, the Forever Lovely Rose and the other, more gruesome headpiece from the ‘Love is in the Air’ festival, Vile Fumigator’s Mask, are both un-transmogrifiable.

We will endeavour to create a Blacklist of un-transmogrifiable items which, even though they adhere to most ‘mogging guidelines, fall at the hurdle of the ‘absurdities rule’. The list will be added to our Transmogrification Rules article when we’ve compiled enough information.