I have only seen the movie once and liked it, but I agree with a lot of the great ideas here, especially from The Aluminum Falcon. As mentioned, only seen once, so pardon the question: Would removing the mind-reading tentacle alien create some plot hole? Can’t exactly remember.
Also, would you only remove the scene with Vader and Krennic in Vader’s castle, or also the Bacta tank scene? Maybe the latter cannot “stand” on its own, without any conclusive scene that explains what we just have seen and why.

In my current idea, I would start at the view of the Ring of Kafene, then directly jumping into a scene where the storm troopers rush to find Cassian. Maybe even skip that he killed the informant. In another spoiler thread someone suggested that he would look too evil for the viewer if he commited homicide at the beginning of the movie, which would hinder the viewer to build up sympathies for Cassian and also not killing the informant would explain better that he hesitate at shooting Galen.