For Lexan and cast acrylic the optimal settings are very non-intuitive.  Has to do with putting the heat into the chip and not the tool, so it won't mark the part.

I had to "fix" a larger more expensive part once.  The 3M stuff you get for cleaning up car headlights can do amazing things for fixing and polishing scratches on lexan and cast acrylic.

I don't do much aluminum on CNC at this time.

I have been involved in electrical and somewhat in electronics since 1962 and also air craft electrical.  100% on crimped connections and extra flexible wire.  One other thing, they do make stepper motors that have feedback like servo motor encoders. I looking into it at one time and they were not much more expensive than regular steppers. I will try to post a link if I can find the source.