Alright, let’s see what we can do here…
Firstly, here is a question with some Blender FBX export settings: Blender to UE4 import question.
Secondly, you are right to create a second UV channel for the lightmap. Make sure this channel has no overlapping UVs, as that will cause lighting issues. Blender also has a default way to create lightmaps, if you haven’t done so already try using Lightmap Pack when generating the lightmap UV layout, and set the margin to as small a value as possible. (You may already have done all of this, but I’ll put it here anyway just in case, and in case it helps someone else).
Lastly, assuming you are using Blender 2.75 or later, the import settings should be pretty straightforward. Try the settings from this thread if you haven’t already: Blender to UE4 export and import settings. I’m pretty sure that the added rotation upon UE4 import shouldn’t be necessary anymore (just remember to use the -y direction as forward in Blender). The info is slightly outdated but still very useful and well organized.
Best of luck!
-Noah