Plant looks great, but in my opinion you have a ways to go. That’s why buds look so small, they’ll get quite a bit bigger.
When you start seeing majority of pistols going to darker colors, then you can start looking at the trichs go from clear to cloudy to amber. You’ll want to harvest based off of desired condition of them.
As far as general rule for cutting stems, I’m not aware of any. Don’t try to cut them with your trimming scissors. A heavier jaw garden shear usually works pretty good.