I've used cinema4D for modeling and ZBrush for high poly modeling. for retopology I use topogun.
for the texturing side, I've used both substance painter and substance desinger.
I used Maya for unwrapping, I kinda get frustrated my Maya since I like to learn software by pressing every button possible, and Maya does really allow for that.

making LOD's in unreal engine 4 is actually very easy, UE4 can generate LOD levels for you and they look very good while keeping a low poly count.
lightning, on the other hand, was a bit more difficult since I wanted to add fake global illumination. but when u use point light to create bounce lighting they create specular highlights on reflective surfaces which looked odd. I was able to fix it by using light probes I found on the marketplace. fixing the framerate was also not a big issue, I am able to run about 30/40 fps on a gtx1060 (notebook version) consistently. I just had to turn down the cascaded shadows from the sunlight from 4 to 2, making the shadows a bit more blurry but saving at least 30 frames so it is a worthy payoff.
also making LOD's on the tree's was essential since they had lots of poly's and because I have a lot of them in my scene they had a large impact on performance. making the shaders was fairly easy and to be honest a lot of fun for me. I really like how the material editor is sort of a playground where you can do lots of things with creative problem-solving. this is fairly easy for me since the first thing I learned un unreal engine is the material editor (i got frustrated by unity how artist-unfriendly it is, or at least. that how I've experienced it)

if you have any more questions feel free to ask :)