On the feelings part, there's a lot to wonder about when it comes to Mind Flayers.
Ending spoiler:
If you choose to become a mindflayer, the narrator mentions how you are now free to manipulate your friends and former companions. You can choose not to do so, but that the thought even occured shows (imo) that being a mindflayer comes with some... let's call them alignment changes. When I heard that line, I suddenly had more understanding towards why the Emperor acted the way he did. The Design at all costs (not The Grand Design in his case, but the Emperor had some very clear goals and he let NOTHING stand in the way of those goals. One of them was to survive, which is why he killed Ansur and why he chose to join the Elder Brain when he was 100% sure that Orpheus would kill him. The Emperor manipulated Tav into thinking that Orpheus would be unreasonable and violent, but honestly I think he was just afraid that Orpheus would kill HIM for everything he had done to him. Not an unreasonable fear.
If I remember correctly, the dying Mindflayer you find at the beginning of the game is not only adept at forcing (realistic) feelings into Tavs head, but his body language expresses also feelings (which the narrator comments on). So I do think that they do have feelings. If we're to go into real world psychology and biology a bit, having feelings is a massive boon to survival in animals. It would be strange for them to not have any, unless each individuals every move is directly controlled by the Elder Brain (which iirc isn't the case).
Also
So they don't have souls? How come we can use Speak with Dead on them, then? (it calls the soul back to the body to answer questions)
