I made the ride from Honor Hold to Shattrath, it's actually pretty easy and there is really only one tricky spot. About halfway, a nest of level 63 Ravagers will crowd the road. If you try to ride past, like me, you will most likely die. I suggest if you have stealth that you use it. I did that on the second attempt and none of those big ugly critters paid me any notice.
Here are the portals in Shattrath. These will take you to Darnassus, Stormwind, and Ironforge. In this same area is a portal to Exodar, and portals to the Horde capital cities. The first thing to do is make Shat your home and use the portals to visit major cities. So, for the first time since day one, Darnassus is not Keila's home base.