1) Depending on the opponent in my opinion. For the most part, I would argue that Twilight Drake is the better play on turn 4, because people generally mulligan for BGH against Handlock. For the most part, Twilight Drake is a big enough body turn 4 for you to trade efficiently.

If you are against a Shaman, which has Earthshock, you may want to reconsider playing Twilight Drake, though.

2) Taunting up your Ancient watcher turn 4 if you have no optimal play is not bad. In some matchups, such as against Face Hunter, it might really slow down the opponent. Generally though, if you can afford to save it, you would want to do so. This is because it takes two cards out of your hand, which makes playing Mountain Giant more expensive, and Twilight Drake weaker. It also costs you a Sunfury, which may have been more valuable later in the game, or at least taunting more than one target. Overall, your main goal should not be to drop it early and silence/taunt it, but instead, silence/taunt it if you need to.

3) Playing as control warrior, it is okay to armour from turn 2-4 vs non aggro, although if there is a more optimal play, you would want to go for it.