Go to the atmosphere Properties and add a transition with night as day time.
e.g dlc/mud_road_gloomy, set "hold" to 0 (seconds) and "transition" to 0. This way the lamps should be on ingame, however you won't able to use your own atmosphere settings, maybe some experts can help you more than i can.
you have to use an action marker and attach rain sound to it. But even this sound is so quiet, that you won't hear it over the ingame music. The alternative is to use the ambient sound properties.
I wont change the basic layot of the original, sorry.
Especially until the real issues are sorted out.
The economy in COH2 works different compared to coh1. To keep the resources like this will end in 5 min t70 without industry commander. This map will be a true spamfest for vehicles and abilities.