hard time deciding class make up to begin with...

[Mac]

So you have
Account 1.70 Druid Tank
Account 2.70 Priest in S1 & Shadow gear
and 3 more new accounts?
Account 3
Account 4
Account 5

I like the idea of creating "alts" in each account that does different thing then my main. And each character would have a Primary role, and Secondary role (tank, healer, dps).
So, Account 1 have a Druid tank 1st, and Healer / Boomkin, 2nd. I'd roll a DPS caster class like a mage/warlock.
Account 2, Priest is DPS 1st, and healer 2nd. I'd consider rolling a tank in this spot, but not yet since you have 3 other accounts. I'd stick with a DPS spell caster class like a mage/warlock.
That leaves 3 accounts.
Account3.Tank
Account4.Healer
Account5.DPS

Thanks for the suggestions on account and questing strategy. Currently my Druid and Priest are on the same account. I was having this conversation to try and decide what to do with them. If I re-spec the priest holy, I'll move him to another account so the druid and the priest are on separate accounts.