Creating A Mold Of My Old Retro Computer's Case

I am into retro computing and retro computers. I want to take the plastic case off an old Commodore 128 personal computer. Then I want to create a mold of this case. Then I planned on greasing the mold or whatever is recommended and mixing up plasticast resin and ink from a green highlighter.

Btw I tried this part as proof of concept and it worked great. mixed it slowly until the color blended evenly and it did not affect curing at all. I used a small amount in a small teardrop shaped rubber mold. After it hardened it was translucent green and glowed by a black light which was what I wanted.

I want to cast the plastic case in this green resin and then tap the screw holes with a tap set. Then I want to do the same for each keyboard key. I have rub on letters for the keys and plan on using a single drop of clear fingernail polish to set the letters so they dont rub off with use.

I have done the rub on letters before because I lived in Japan for a few years and and I added Katakana rub on letters to my keys and programatically made a switchable character set for this. The nail polish worked great.

Here is my question. What is the best way to make a mold to best replicate the case? While rubber molds might work well for the keys, the case is larger and very thin plastic so I think using rubber would be difficult because it flexes which may cause the final molded pieces to be wavy or crooked.

I have never made a mold of anything. I can practice on something first, but please be very specific on how I can make this mold.

If I can get this to work, I am going to mount many blacklight and green LEDs inside the case and some will be connected to the audio output and produce a light show that is sound driven along with power on and drive indicators. I am updating it with VGA and SD card reader to get rid of the old TV out video and the floppy drive.