SPriest is actually a spec I know little about. But, it's not like the old days, every class/spec is viable to a pretty good degree.

The only other thing I might suggest is to go 2 Priest, 2 Shaman. Just so that if you ever want to, you have some class/role flexibility.
So you can respec the Shaman to resto and Priest to DPS, in the future if you get tired of the other way around. Or, eventually turn a Shammy Enhancement and give melee a go too.

Priest is the only class to have 2 healing specs, so if you had 4 and got tired of/didn't like Shadow, you don't have much room to move.