4. You mentioned the addition of a third party auditor, is that not redundant if the player can follow the hash chain and see crash results locally for themselves? What is the purpose of that addition?
I'll be acting as the third party, so perhaps I can speak to this. What devans wrote above is a great answer. But to add a bit more context, the main benefit of a third party auditor is actually for bustadice. On Bustadice ActuallyFair will be able to provide a significant amount of guarantees, this is because ActuallyFair is given and records all the bet information before the outcome is provided to bustadice. However in bustabit this is not possible because players are able to cashout after bustabit knows the crash point.
So more practically ActuallyFair was used to provide a lot of value to Bustadice, and it sort of just makes sense to use the same system for both even though the benefits to Bustabit are more minor.