I'm assuming that we have probably seen all or at least most of the Origin Characters. These characters have more lines of dialogue than anyone else almost definitely, and require the most work toward developing in general. I'm assuming that later in the game, possibly after the end of Chapter 1, we will be introduced to more potential companions who are also heavily developed, albeit to a lesser degree than the Origin Characters (who, to remind you, are also player characters).
Nope. There will be more companions added throughout Early Acces - and EA consists of chapter 1. Having to pick your team from available companions/origins would be in line with what Larian did in D:OS2 as well.