I agree with what you are saying completely. I plan to only keep the case and back and replace everything else. I would have loved to put a mechanical movement in the watch but I think it’s too small (33.9mm x 7.1mm).
My plan is to have the case and back replated and have the back blanked of its manufacturers engraving so as I can have a blank canvas to have something engraved on it myself. I was hoping to get advice on what movements could be used and buy the parts ready for a watchmaker to assemble as like you said, I don’t want to ruin the watch.
I’ve already started sourcing/ordering parts which was a little silly without any advice so I’ll post what I have ordered below (if rules permit me to do so?).