Roughly a couple months of baking...
Continuously? As in, 24/7? 
... couple of months of generating the new required UVs ...
I think I saw it being mentioned in a tutorial somewhere that UE generates its own UV maps from Ninite created meshes. (?)
... adding a couple hundred gigs of new lightmaps to your game ...
Why would this happen, though? Seems a bit excessive given many other older games with big open worlds have baked open world lighting. Or is that an Unreal Engine thing?
... The foliage is already not transparent ...
Trees and tree branches seem to become transparent (that ones you can move through), when I get close to them. Their movement animations also seem to be very low FPS up close (like, 10 FPS or close to it...).
As for the dithering, I have indeed noticed that. Kind of why I haven't been able to get the game setup with decent graphics and FPS. It's always either bad visuals (low and blurry textures, even if they're set to Epic, lol) with decent FPS or low FPS + high latency (Frame Time ms) and "decent" visuals. Would've used "Frame Generation" (
) but it messes with the holo scopes and lasers.
... Adding LODs won't result in any performance gains and would rather degrate perfs since now the Virtual Shadow map system has to rasterize all of these instances instead of reusing Nanites acceleration structure.
I'm not gonna pretend I know much (I know exactly shit about fuck), but according to some videos I've watch (one of which is this one for example: https://www.youtube.com/watch?v=Ls4QS3F8rJU), generally speaking LODs seem have better performance when it comes to sub 50k triangle meshes, while Ninite's better for higher ones.