I can answer the second question:
Generally, hot-blooded mammals transform 90% of the energy they get from food into heat.
So using a cat for heating your room is about 90% as effective as burning cat food in an oven.

Here's some napkin math for where I live:
1kg of firewood has 4kWh = 4000 kcal
which is about equivalent to 1kg of really cheap dry cat food (mostly carbohydrates)

1kg of firewood costs about 40 cents
1kg of cheap dry cat food costs about 1,20€

So, cat-based heating is about 3.3x more expensive than burning pre-dried, commercially purchased firewood.
(all of these prices heavily depend on how much you buy in bulk, though. And if you care about your cat's well-being, you're gonna spend 2x more on its food)