"What exactly are the effects of cooler weather on the plant?"
Cooler weather helps the plant develope Trichomes

You mentioned "late trichomes", sometimes that can be caused by the type of strain you have(mostly means the strain is weak), it's really nothing serious..just keep growing because some plants start slower than others and some plants develope Trich late and then it BLOOMS....so you might just have a late bloomer...

Darkness & Cooler weather helps "thc".....Just don't freeze your plant(s)