Is there any kind of damage formula for criticals?

Is the number for critical damage on a weapon a static amount, or does it scale at all? I know that weapons like daggers and bandit knives are typically for dexterity builds, but I was wondering if there would be any benefit to using one as a mage. I was thinking I might make one that is Enchanted. Would I still get backstabs comparable to that of a dex build?

Yes, because if you use it enchanted, it will scale with your INT, not your DEX. I have a enchanted estoc which scales A with INT, can't confirm right now how much scales with DEX

^ barely noticable stat bonuses from both str and dex.

Magic/enchanted/divine/occult weapons are there to change the stat scaling from str/dex/both to either int or faith. This is useful if you plan to have minimum str/dex and focus your stats on int/faith. Of course, str and dex both have their uses (str bonus benefits from 2handing a lot more, and dex speeds up casting of sorcery/miracle/pyro). So unless you really want to stay under a certain SL and focus on int/faith, using normal weapons and having some stats in str or dex is always useful.