This is honestly the approach that’s given me the most peace of mind as I’ve gotten more years of GMing under my belt. As little as possible, but at least something for everything, so I’m never truly caught of guard by player shenanigans.

Me, personally, I have slowly started to shift towards “bones-only” storytelling for my campaign settings – I build a loose plot, some NPCs tied to it, locations and a few bigger encounters. Beyond that, I want my players to not feel railroaded to encourage them to think creatively in each session, as it helps me as a GM enjoy the session more when players aren’t always looking to me to tell them what they should do next. I also usually stockpile a bunch of pre-baked generic encounters, NPCs, shops and such so that I can keep up with their story and choices.