Yes, the curve implementation is good. Much simpler without the Bézier control points.
As for the fonts, I did a little experiment. I fear the symbols/fonts may not survive in a transition between platforms (or are there native Java fonts that would work?).
My test became pretty messy, I tried using multiple same elevation levels, but must get used to how best to work this to switch between normal and construction elements (and then I really do not know how to do technical drawings in the first place).
ok
Test file: test_symbol_drawing.sh3d
Result (pretty messy, but shows concept):
