You can add points directly to Intelligence in Attributes tab to unlock Brainy.For me the main reason to pick any of the skill classes is just to meet the minimum stat threshold to pick the traits I want. I would probably go with zero skill classes if not for that. For now I've been taking expert slaver just because I STILL haven't done Adora's quest yet and I want to see it. Other than that I take soldier so I can pick Deadly Strike and either Doctor or Scholar so I can take Brainy.
Personally, I don't think Z Mark is worth 50 points. The 5 health and stamina restored during night is only useful in the very early game and extra stats are kind of meh, as you could instead pick disciplined to speed up training of all basic skills.
Disciplined is of course not strictly needed, but I think it is a good choice when I have some points to spare.