My question is specifically about the interaction between Spiritbane and Spirit Armor; if I have Federin Starsdawn equipped with Spiritbane in the same army as Geddion with Spirit Armor, is his range 12 or 14? Thanks in advance!

It's on the rulebook.

simply, Always change the value before a modifier.

so, his range will be 12 + 2 = 14 pol

I don't think it was in the rulebook itself (I'll double-check), but it was almost certainly in the FAQ if it wasn't :)

Replacement values happen before modifiers. Multipliers are considered "replacement values" (and if you have two things that replace, you have to choose which one to use).