It indeed comes with moon lightning, it really has tons of options and as I remember you can also set how much moonlight there is, the angle, color, etc.
I can’t really give you a definite answer about how performance heavy it is, it’s probably better to ask the Maker of it (he’s a nice guy and usually replies very fast). But it has a few options for the quality level of the volumetric clouds, the lightning, and all the stuff that affects performance, without (in my opinion) looking bad on the low levels.
I saw only a few fps (like 2-4) drop in my project, but that was in a rather empty scene without a lot going on. I yet have to test it in a heavy load scene. So I think it really depends on how you set it up.
My guess is, as you’ve a talented developer in your team already, he should be able to tweak it enough to make it usable without a big performance loss. And you could always just use it for the very customizable day & night cycle and maybe the weather effects, since your clouds look really nice already and fit your artstyle very well. Or just use it as a base to build / expand your own system.
Hope that helps. (: