Also as kind of a tertiary question to your suggestions, Nodoze:

What would the second lock bring to the table that a second mage wouldn't that would make a massive difference? Or is it more personal preference?

And:

I love the thought of a shammy healer rather than priest so that mail/spell leather doesn't go to waste. From an ease-of-use standpoint, does shammy seem to be much harder than priest or about the same? I leveled a shammy in a melee cleave group 5 box and it was simple. But never tried with caster nor as a major contributor to defensive things like grounding totem, etc.