Any way to adjust my night to be brighter, such as PreferredEnvironment from Chaos?

The plugin already makes night bright, you can adjust the weather variables to try and make it brighter in the weatherAtNight config.

I forgot to put my 2nd question, which one means what under Config?

These are all of the available weather variables, you can use weather.atmosphere_brightness or weather.atmosphere_contrast to adjust the brightness.

weather.atmosphere_brightness
weather.atmosphere_contrast
weather.atmosphere_directionality
weather.atmosphere_mie
weather.atmosphere_rayleigh
weather.clear_chance
weather.cloud_attenuation
weather.cloud_brightness
weather.cloud_coloring
weather.cloud_coverage
weather.cloud_opacity
weather.cloud_saturation
weather.cloud_scattering
weather.cloud_sharpness
weather.cloud_size
weather.dust_chance
weather.fog
weather.fog_chance
weather.overcast_chance
weather.rain
weather.rain_chance
weather.rainbow
weather.storm_chance
weather.thunder
weather.wind