>1. What is the biggest difference between living in DC vs visiting DC?

As a DC resident, you have no representation in Congress. That's a pretty big deal.

>2. I'd love to be able to not own a car. How doable is that?

Entirely doable. The DC Metro system is not as reliable as the NY Subway, but it works. There are buses all over, too. You can basically go anywhere within the city or the adjoining suburbs using mass transit, and there are plentiful bike lanes if you are a risk taker.

>3. For people who are familiar with both cities, how would you compare DC vs NYC?

People here are less considerate. It's less convenient for commerce because almost nothing it open 24-7 anymore.