Not necessary, because the conclusion is limited to those people who DO want a dog; how likely someone is to be one of those people is irrelevant.

Necessary, because if this were not true — if providing a dog with more intensive exercise does NOT require more time than providing a dog with less intensive exercise — then the fact large dogs require less intensive exercise would not establish that they require less time to exercise. And in that case, we have no reason to think that someone with limited time would find a large dog less troublesome to raise.

Not necessary, because whether someone “should” or “should not” own a dog is irrelevant. The argument concerns what kind of dog would be more troublesome to raise. Whether it’s a good idea to own a dog or not is a separate issue.

Not necessary, because the argument never compares dogs that live in “large apartments” to dogs that live in “small apartments.”

Not necessary, because although we know that dogs require a certain level of exercise intensity to stay fit, that doesn’t commit the author to believing anything about how “often” a dog gets exercise. We don’t have any basis to think exercising once a week for 2 hours is any different from exercising 4 times a weak for 30 minutes each time.