WoW SoD Gearing Boost & Carry

Both exist. BiS Gear Boost is a bundle, and many drops such as Darkmoon cards and single weapons have their own offers.

Yes. Overgrowth, Sandstorm and Torment each have an offer, and a deck offer covers the full set of cards.

State your class and role on the order page so the pieces you receive are useful for it.

Drops are random, so the player keeps working the source until the item is awarded, as described on the offer.