ChanceToHit is the stat that corresponds to how much of a boost (or penalty) your accuracy gets. The default difficulty settings changes the ChanceToHit depending on if you're in Easy or Hard for both players and enemies, using the very same Character.txt stat entries I'm using for a global change. Beyond that, certain skills can change this value too: Bless gives +30, Precision Stances add 25, Power stances give -15, etc etc. Those stat changes from the skills are described in the Potion.txt file. There is some sort of penalty tied to levels I believe (attacking an enemy 5 levels above you is tough), but I don't think that's moddable. The boosts I have mentioned above are flat % boosts independent of level.

I don't think I can touch the talents at all. When I tried to change the requirements via my mod there was 0 effect on their requirements ingame. Maybe this will change later, but for now I'm just leaving them be.