Afaik it's already planned to give us both the option to create a custom party at the beginning and let us hire generic customizable mercenaries later on.
Thanks for the info

You don't happen to remember where you read/heard it by any chance?

From the March AMA, so could be outdated, but I don't think anything changed in this matter:
Will all possible companions be available as Origin character options or will there be companions available only as NPCs?
Swen: We are trying to make all characters with backstory available as origin characters. Other than that, you will be able to recruit generic mercenaries and customize these. We’re also planning to allow you to build a custom party from the character creation screen though that most likely won’t be present in early access from the get go.