Interesting thought, to change the negative version first. I inverted it back to positive as a first step, my reasoning being that the inverting process should be a simple mathematical process, not prone to degrading the information. I could be very wrong there though. You also mention colour noise and a magenta cast. I didn't think to do a white balance, and going further back, I could have also set the camera to black and white, but didn't. Don't know if that would make it better or worse.

Keeping notes would be a good idea, as it is easy to get lost. Also, if you come back to it later, after years for example, it will be almost essential.

Whatever else happens, I got to try some film in a very old camera, and the project has turned out to be a success inmy estimation. Thanks for being interested and helping.