I got both Caster and Overload but im using Caster on my meta pyro. It has better damage output for me and i dont need to cast magic shield that can drain SP in 10sec.
Tho your choice. Overload is cheaper and works with every build so yeah, if you can share gears, overload is the best choice…or atleast a temporary while building your effect-specific ichors.
For wizard staff…i only use pyro vaivora for all my wiz. It has good base stats and my other wizards have shitty vaivora (i got terra-omnyo, and rune-omnyo-terra)