Well the biggest third-party keyboard of the lot, SwiftKey, has all of the features I listed.
I genuinely don't know what would make a good tablet keyboard, despite having owned a tablet for 6 years. They are too big to thumb type on like a phone (certainly in landscape mode - I rarely use mine in portrait) and yet vastly inferior to a laptop for proper typing. None of this is an impediment to me as I mainly use mine for reading and annotating documents using a stylus, but for typing it's the least favourite of all of the devices I own. I were going to do a lot of typing with a tablet I'd personally use a physical keyboard with it (but then I've touch-typed since the 1980s, so that will always be most effective for me).
As you say, perhaps someone else will have some other ideas.