I thought about adding a script directly to a perk instead of adding an ability which has an effect which uses a script, but I'm unsure when a script that is added to a perk actually runs. Immediately? Do the perk conditions have to be met? What a bout the perk entries?

I'm sure I could figure it out with some testing on my own, but I thought maybe somebody already knows this ...

I am pretty sure you can't add scripts to perks directly (thus even the vanilla perks use the ability workaraund or entry points where applicable) the script window is there but the buttons are all greyed out.