Yes, as everyone is saying, we’re expecting to have to start again from the beginning. But on the plus side, we’ve been told that there will be lots of surprises in Act 1 even for early access players, so we won’t just be doing the same thing again. And wouldn’t want to miss any of the new and changed stuff anyway!
It’s not possible to respec our characters in early access. It’s possible we will in the full release, but as far as I’m aware we’ve had no official word on this.
And it is in early access possible to get two custom characters in the same game, but only by setting it up that way from the start. It’s also a workaround and doesn’t work perfectly. We are expecting a more official solution for the full release but other than a hint about “hirelings” on Larian’s Twitter we don’t know much about it.
I wouldn’t expect us to be able to import a character from part way through one game into another given their stories could be incompatible. Though I guess it’s not impossible that we could be given functionality to export our own characters and use their build for hirelings or other custom party members, we’ve not had any hint of such a feature to my knowledge.