I would imagine you would be fine with that selection.

Couple of things to keep in mind.

Running multiple classes doesn't seem too difficult to me so far. However, since you are effectively AFK for the most part some classes will never maximize their DPS output when they are slaves. Some people may be able to do it, but I wish I knew how. You have to pay attention for random events to occur and then take the appropriate actions to maximize damage. So, some classes may actually be much easier to maximize their DPS. I never played a hunter, so I am not sure if this is one of those classes. Also, consider what utility other classes may offer to your group [for instances] before you choose all of a single class (not that it's bad or incorrect, but you don't want to regret not having a shaman or something down the road). Mixed classes can also be good for loot distribution too(i.e., cloth, mail, leather, plate classes). Of course, on the other hand having multiples of one class offers other benefits and MANY multiboxers have been very successful running 5 and 4 of the same class and spec.

Also, there isn't much point in your priest going holy until you really need it. Unless that's your preference, you can still DPS etc. However, you will probably be fine as shadow for a long time if you want to maximize DPS and still be more than adequate for healing. Leveling through questing is really easy though, so in the end the point is moot. You could level up a group of five naked toons that have never spec'd a single talent pretty easily I imagine.