I recently ditched my 1pally 4shaman team the other day and made 1pally 2lock 2priest. I don't have a mage in my new setup because I wanted an additional offtank for my paladin (void), while the other lock uses an imp for blood pact. I wanted two priests because I can either have two shadow priests with their stacking buffs which does wonders for my paladin, or one shadow priest and one healing priest.
I assume when you are playing this setup your goal lies in PvE and so in Heroics some day? If so I would assume that you will get destroyed easily by all mobs there witout any CC and the void walker isn't quite a good replacement for that but tbh I never played much heroics before so I could be wrong here, the Idea itself is pretty good. I would rather play something like this:
1 tankadin / 1 healer (priest would be good I assume) / 1 warlock to be the shadow whore (main DD) / 1 shadow priest for even more shadow damage and mana regen and finally 1 mage for CC only, water and all that stuff is just a nice give-away.

Not sure though if that would work in any way.

Xorn