I definitely don't want to say that it's easy, but it's not terribly difficult. Does take a shift in thinking though, but then it clicks.
For reusing sketches, you can. There's external geometry and subshapebuilder. Doing assembly can be a bit tricky at first.
I'll admit, FreeCAD is a bit tricky if you're coming over from something more professional like SolidWorks or CATIA but it does get the job done and you can't beat the price. It's also really improved over the last two years