You're really over thinking this. I think the easiest way to defeat Gaia and Gaia 2 is to just load up on Runic Shielding items or TiCon hearts and some sort of perma regen (potion works) then blast away with a silverwood staff + shock focus.
FYI - 4 pts of potency and 1 pt of chain lightning in a shock focus in a silverwood staff will do 5 hearts (plus jump to other mobs) and will fire something like every 0.3 or 0.5 seconds and it never misses. That's right, it auto-locks on target so long as you point it in the general direction of the mob you are fighting.
Even though the per shot damage on the staff isn't that high, the rate of fire and the fact that it's ranged and never misses means that it does a lot of damage per second, plus when he goes into his static phase where he starts spawning mobs, the staff will AOE burn them all down without you ever getting touched as it will stun/knockback them.
I honestly think this is the fastest way to kill him (at range) because even when I build underground and chase him around in a small room with a high dmg sword, it still takes longer than zapping him to death with a wand focus.
