in the book, the problem of exposition was solved by providing the characters with an inner monologue/voice. The Lynch movie tried to adapt that by making it a literal voiceover from each character. I wonder how this movie solved that problem? Probably why they needed to split it in half. Splitting it in half also allows them to flesh out the battle scenes.
The hook to this movie is going to be early on, when Paul sticks his hand in the witch box to get tested. If they nail that scene, the audience will buy into everything else.
I like your ideas about HAL. It occurred to me that HAL had become self aware about his own mortality and is becoming paranoid. This is implied by the conversation HAL has with Dave where HAL is probing Dave how much he knows about the mission and Dave shuts down the conversation with the crew psychology comment. Immediately after that comment, HAL announces the failure of the AE-35 unit.