I'm going to have to give FreeCAD a try -- does it keep a timeline where to can go back and make changes to previous design choices?

Can’t remember about timeline but you could probably manage to use git even if through sub modules. Cool thing about freecad is that it allows python scripting :)

It does. Although not all steps can be changed without consequences. Working this way is a bit restrictive but if you set up your model the right way it a pretty good tool.

FreeCAD is excellent. The learning curve is steep, especially so if you are coming from a proprietary CAD software... But once you find a workflow that works for you, it is incredible for parts for 3D printing and lasercut panels, with no licence hassles.