The future is looking promising for Freecad. Assemblies have always been a problem. There are three different third party assembly workbenches currently available but there is no guarantee that they will continue to be maintained. At last an assembly workbench is being worked on that will be integrated with the main program. No release date available yet but here is a preview:
https://www.youtube.com/watch?v=MI2JMm__bkM
Russell