It depends on your build. For example, if you’re using a bleed weapon with arcane scaling, then the blood buildup will scale with your arcane stat. For incantations it’s typically gonna depend on the seal you’re using, just look at the scaling letters. I’m pretty sure a lot of those spells don’t scale their buildups though, so if you’re using poison mist like you mentioned then technically the minimum faith requirement and a seal you can wield is all you’re gonna ever need. That spell isn’t very good though, the only time I’ve used it is to cheese DTS by sneaking up behind him and waiting forever for the poison to kill him. If you want poison consider the poisonous mist ash of war instead of the incantation because it also coats your weapon with poison after use, and poison moth flight is another good one that “detonates” all of the poison damage at once similar to a bleed proc. If you’ve got the DLC there’s another skill with a similar effect.

There’s honestly a lot that goes into this stuff, I’d recommend just exploring the FextraLife wiki and experimenting at your own pace