I'm intrigued by this "Night card" idea, because I don't understand what design space that would open up. Venture is kind of like a peddler that you play during the buy phase and that's not too exciting, but I expect Night cards are going for something different.
Perhaps Night cards will fill a design space similar to events like Donate, Mission, Scouting Party, Bonfire, Save, etc...
So, trashing, sifting, extra turns, doing stuff for your next turn. Maybe also gaining and attacking.
But I'm not sure what purpose it serves to do these things after your buy phase. If it's to set up your next turn, there are durations for that. If it's to trash or attack, what difference does it make whether you do that before or after your buy phase? Sifting, hmm.
Maybe the main thing is that the Night phase comes with a separate supply of +Actions. So even if all the actions are terminal you can still play two per turn, provided one of them is a Night card?
Come to think of it, we don't know whether Night comes before or after cleanup, that makes a huge difference.