It's posible to have an ending where Caed Nua is kinda rubbish (Security < 30, Prestige < 30)
I'd like to see prologue to take place in Dyrwood, setting the stage for a great Deadfire expedition.
I think they've already said that the prologue will take place in the Dyrwood, since you're departing from the Dyrwood.
I hope we don't have to do any sort of Oregon Trail style stocking of supplies first though. Obviously there would be supplies needed for the journey, but we shouldn't have to worry about specifics. One of Sagani's endings says it takes four months to get back home, so, four months is a good max amount of time, perhaps two months with favorable winds and currents.