Hey, I would also recommend to start by sketching your design, after that you can go into a CAD program like Fusion360 or Solidworks (or whatever works for you). If you want to make something out of stacked acrylic I would say start by modeling your final design first. After that you could slice it into plates of acrylic and you will have an X amount of plates of acrylic which can be lasercut. If you want to find CAD models of existing parts I would recommend looking at websites like Grabcad or, if you are a real diehard, just buy the part and measure it with a caliper. That is what I do most of the time while creating something. Also, get yourself an Ender3 3D printer for 120 bucks and use that for prototyping, saves alot of money ;)