@happyopi I think you can buy perks from different branches, it's just that you need the lower one to get a higher one. I haven't seen anyone go into details about that yet.
I got a little bit worried when I found out we can't choose the quirks, but it looks like there are ways to control which ones our sim ends up with and even an option to clear them. Overall I'm pretty pleased with the system from what we've seen, but have to try it in action to see how it really feels like. I will probably opt out of the whole thing with some sims in my rotation.