I would recommend the following.
Do not import several CAD files and save them in one layout. Instead, import each CAD file separately, save it as component, and then use the component in layout.
Connect a source of files to the eCatalog. I would suggest those collaborating connect the same source. If that is not an option, consider turning off “Include components” when working on the layout, and then turning it on when you need to save version of layout that needs to be shared. That will keep your backups relatively small in size.
Work with a drawing. If it is a layout, use the Drawing tab to add drawings and annotations to mark things up for review and make comments. This could also be done to avoid making changes to the 3D model itself until they are needed.
Consider using comparative tool or making one. For example, you could make an add-on that compares layouts and/or components, e.g. to print the differences or visualize them somehow. I have never used WinMerge for this, so not sure if that tool can be used.
Agree beforehand on naming conventions and how to share revisions. A lot of time is wasted in my experience when this is not done in advance.