Chuckles. Just had to laugh at your post in an OMG been there kind of way
Well truth be told still there too
Karma our cat 18lbs of a beautifull Maine Coone cat does have all his claws, and he and our big BRT 120 odd pounds both rule the roost. Karma taught Magic how to stalk prey, Karma knows how to open sliding doors (the brat!) and they have learnt to co-exist to the point that if Karma is laying in the big boys crate, Magic will let him have it and just lay down in front of "his crate".
Not so with our spitfire of 6.5 lb Yorkie. He constantly chases the cat, and Karma never, ever backs down. They have a good game of chase, then when Karma has had enough turns on him, and bats him silly. No claws ever extended! Or Karma jumps up to his climbing tower.
And yes they have never slept together, although Magic and Karma have in the aforementioned crate.
So far if I sense it is getting serious, I do break it up, and now Razzle is not always the instigator, sometimes Karma wants a serious romp and play fight time.
They will co-exist in time, but you always keep an alert ear and eye out for spats.