Re: pronunciation vs accent
I think, generally speaking, if a group of people (from the same region, the same socio-economic class, etc.) pronounce things in largely the same way, they have the same accent.
If an actor is playing someone from the deep South in the US, but sometimes he pronounces words the way they do in the South and sometime he pronounces them in the correct manner for someone from New England, he is not necessarily mis-pronouncing words, but he is doing a terrible job with the accent.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.