Hmm… It might be a big change to incorporate, but you could perhaps look at RenderPipeline.
While I haven’t used it myself, and thus can’t speak to whether it does quite what you want, it looks like it might well do at least some of it.
I’m not sure of how this would interact with fog, but could you perhaps just use simple quads with an image of a light, oriented to face as appropriate, and set to be unlit?
(Perhaps with a billboard effect to make them turn towards the player, and a bit of control code to set their alpha-scale to some value related to the dot product of their current direction and their “forward” direction.)
Not to the best of my knowledge, no. You might want to look for middleware solutions for that. (If you don’t want to build your own, of course.)
(Although I see that one of the screenshots on the RenderPipeline (see above) GitHub page depicts a lot of trees. Whether it has built-in support for such, or that’s a specially prepared scene, or what, I don’t know.)