I can second that. I spend a lot of time in Detroit and its suburbs (though don't live there) and have yet to feel unsafe despite dire warnings from all kinds of people. There are definitely areas to avoid, but that is equally true of New York City or San Francisco.
Not even areas really, just activities. Don't get involved in gangs or drugs and you'll never have any problem. One nice thing about the Motor City is that sidewalks are empty, because if you had any money you would be driving. I've walked and biked all around the city and metro, you're more likely to be hurt by a pothole on a street with no lights than by muggers or whatever people are afraid of.
It's humid and muggy in the warm months and windy/rainy/snowy/cold otherwise. You have to be climatically adapted and motivated to walk around outside most of the year. Plus, car culture is a big thing ("Motor City") so everybody drives and there's next to no funding for public transit. There are sidewalks, there are walking and biking paths that cover a surprising area, but the number of things in walkable distance is very location-dependent.
Somewhat. Downtown is perfectly walkable. Some of the individual surrounding towns are too (Royal Oak for example), but the metro area as a whole is not. I haven't looked (I usually have a rental car), but I don't think the public transit is particularly useful either.
The weather needs to be your biggest consideration. Cars get eaten alive by salt and you'll need one for sure. It's cold 6 months a year and in the winter you get like 8 hours of sunlight, while you're at work. If you are used to warmer climates you'll probably hate it. It is cheap though, if money is your thing.
