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Hi this is Dr. Hill. I t sounds like Mojo has a pretty enriched environment. If he is not urinating or defecating out of the litter box, then I attribute that behavior as an introduction into the room. Cats will paw or scratch when they enter a room. If the behavior is worrisome, then you can put a scratching post at the entry to the room with a sprinkle of cat nip so that he can scratch on the post
I am so sorry about your fiancé. Mojo must be a great comfort to you. I would definitely let him be in the main house with you at night as long as he is not having any issues with not using the letterbox. Many cats are not vocal. I have seven cats and only 3 ever really talk. It just depends on their personality. Cats are pretty hardy about colder temperatures because of their fur. And yes, you can make it too hot for him. If the temperature feels comfortable to you, then it should be fine for him.
You are very welcome!