I observe the plans of a global mana pool with growing concern. I think that the idea of a global mana could put users in a bind if they use it all up in some epic battle, all of their spellcasters would be rendered inert.

A better solution in my humble opinion is to lower the cost of some spells and have mana regeneration as a function of essence. Got 3 essence? You'll get about 1 per turn. Got 40? Get about 5 per turn. This in my opinion not only works better than a mana pot in the sky but makes better sense on the "Lore" front also. The bad Channelers (with little essence) can only 'channel' power at a slow rate whereas the master mancers (with great essence) are, of course, able to channel greater energies faster.

Tell me what you think, feel free to call me names and if this goes down well I may have more ideas.