I think the 13 episode TV series really allows characters to develop and not just an action adventure genre feature film like POTC movies.
A miniseries of 4 or 6 episodes would seem to work but extending it to 12 or 13 episodes spread over a season I think is a great format for complex characters and season-long story and character arcs that are heavily serialized.
I agree. I think a TV series is really suited to this. Movies only allow to skim the surface. They really have a good chance of building up their own mythology here.