I’m not too sure about the skeletal issues, but for exporting I always get the right size with FBX export. I work with the metric unit and scale object to real world sizes, the same size gets exported exactly as is in UE4.
Make sure you have the FBX exporter enabled, the one authored by Campbell Barton, Bastien Montagne and Jens Restemeier, Version 3.7.7 is what I’m running. There was another FBX exporter for someone else, the one I’m using comes with Blender.
In the export settings, use these settings:
Scale = 1.00
Forward = -Z Forward
Up = Y Up
Tick “!EXPERIMENTAL! Apply Transform”
Disable any flags which you don’t need.
So if you’re modelling a skyscraper or mountain, set it to a real world size before exporting, if you want it to be at the right size when opening in UE4. Otherwise you’ll have to set the Scale flag, which could create complications if it does not match the size you’re looking for.