Being that the new update is more critical in nature, I'm going to perform some thread-CPR.
An update (v1.41) is now available to hopefully enable the baker to work again under LW2018. I believe the previous version(s) insta-crash in LW2018. LW2018 testing hasn't been too extensive, so if you encounter any issues please let me know.
One known issue to emphasize due to surfacing being entirely node based in LW2018, also mentioned in the manual, is that using any built-in nodes, like Image and Normal Map, that use UV/Vertex maps will still cause a crash. Make sure you don't have any important unsaved changes. (As with previous versions the PB Nodes, supplied by the baker plugin, are however nodes that can access UV/Vertex maps during baking.)
In addition to LW2018 compatibility, I also added two new options that apply to all LW versions. The first is a global option to output inverted gloss/smoothness values instead, i.e. roughness values. The other is an option to use floating-point image buffers during processing, which gives enhanced precision and allows output of HDR values (if the image save format supports that) it that is required, at the expensive of higher memory use.
All image format handling is done by LW, and unfortunately, AFAIK the LW SDK doesn't expose functionality that allows creation and handling of PSD layers. IIRC LW internally can save out render buffers or something as layered PSD (?), however I assume, that as so often with the internal tools, it "cheats" by not being limited to SDK functionality.
Perhaps it would be possible to create some kind of Photoshop action or script that takes the baker generated Mtl ID map and automatically splits it up into layers? I'm not very familiar with the automation/scripting capabilities of PS.