A resto druid can powershift out of roots, just by being resto.
No talents necessary.
All healer classes can do defensive dispels, to remove things from your own team; I believe druids will have magic (talented) and curse + poison (base).
The first couple of tiers of Feral would be available for +30% movement in Cat Form.



Given the toons you have, and would like to continue (Mage, Paladin, Warrior), I would personally go 4x DK + 1x Pally (Holy); but 3x DK, 1x Warrior and 1x Pally could work too, and wouldn't be that different.

Drive with the Pally (Healer) in PvP.
In PvE/Heroics, if you feel like doing them or pursuing acheivements, drive with Warrior (Tank) or if you go 4x DK's then respec/dual-spec them Blood and drive with the Healer still.

Mosg2's Manifesto basically lists everything you need for the 4x DK + Healer team.
There are even two manifesto videos.