My 2 cents
Plexiglass or Lexan windows are ok for a street car, depending on your willingness to deal with the compromises:
(1) significantly lower clarity amd greater optical distortion
(2) higher maintenance (cleaning & polishing).
For a front window I would go with 5/16” or thicker lexan and plan on regular polishing and more frequent replacement. If you use windshield wipers you will have a lot more maintenance. It is safer than laminated auto glass in terms of breakage and puncture penetration, but it’s probably not as safe if your head impacts it in a crash because it won’t break before your skull crushes. Remember to be careful with window stickers as you can’t remove them with a razor blade. Also, don’t use windex and paper towels (they will scratch). Use something like Meguiars plastic polish w a new microfiber towel ( plastic cleaner and a random orbit polisher w foam pad for scratch removal).
I have had 4 cars that used some combination of plastic front/side windows
They all had fixed or horizontally sliding (overlapping) side windows. Yes, they do get scratched up over time, and rather quickly if they are used a lot. One has fixed Lexan side screens, and they are in amazingly good shape after a full decade of light use. A key factor is they don’t slide against anything and I store them an a protective bag when they are off the car.
If weight savings is really important, I would start with a CF hood & trunk lid (with prop rods), then fiberglass bumpers. The front seats also weigh a lot compared to a fixed-back GRP bucket seat. You could replace your side windows with plastic, but you should go with a sliding sub-window so you can remove the heavy lift mechanism (metal).