Wonderful news, it's now actually worth going about and eating sims for the fun of it! You've made fantastic progress, but the thought also occurs that stomach noises while digesting would be great, or maybe just some wet sloshy noises for footsteps could be fun. I don't know if
https://modthesims.info/t/157145 will help guide you with that, or if it might lead to the very issue that fallout 4's vore mod has where several preds walking around at once just leads to too much noise. Thanks for the belches and digestion, though, that really steps things up! I'll start testing things out and let you know what goes awry or not.
-- edited after a couple days of playing --That said, I am noticing that having a sim eat someone off the street seems to be prone to their prey's ghost just sort of walking away - sometimes off the map - and leaving the pred stuck with a huge belly and nothing to be done about it. Best bet is to avoid eating anyone near the edges of the map so there's time to catch up to them for now. Moving the digest/regurgitate from prey to pred's action options would probably offset that, but I also imagine that'd force some significant tearing down and rebuilding of certain scripts. I'm also noticing any full pred can regurgitate any ghost character, though that's also a bit of an edge case and can probably wait until later.
I'm also noticing that the belch isn't playing after a pred eats someone, nor the belly-rubbing mentioned during digestion; I might be missing a dependency?
A fair number of non-player sims also seem to survive the 'digest' action as ghosts if I stop talking to them shortly after hitting the button. I'm able to regurgitate the survivors by talking to them, and they seem to be miserable afterwards, but eating and digesting them again doesn't seem to bring them down any further. So far it seems to favour characters in public spaces, possibly those who aren't tied to the current location.