What if it works sort of like the FFT Calculator? The cards represent spells you have learned from WHM and SCH and you have to select which ones add. Each card being sort of like a cross class slot, but obviously with a lot less restrictions. The class would have a lot of it owns spells too but a big part would be the spells you take from the other healers.

I also think unlocking these stand-alone classes with probably be quests like in FFXI.