Frequently asked questions...in my opinion...

Check your municipality and your zoning. Generally, if you're in a "farming" district the answer is yes. If you're in a residential, maybe. More and more places are allowing them. If they do it's usually only hens. 

(Sarasota County Florida code as an example) 

The Google answer is; "2 to 3 sf per chicken inside the chicken coop, and 8 to 10 sf per chicken in an outside run". However, local codes would dictate the minimums. 

The reality is it depends on how long they're staying in the coop. If they're just sleeping in it at night and going into a larger run or free ranging during the day, a smaller coop probably wouldn't be a problem. You'll know if it's too small, they get pissy at each other. Give them as much space as you can in the coop and outside.

First of all they're sized to accommodate a smaller number of chickens. Ours are designed with portability in mind. In addition to being required, moving them regularly really does keep the backyard looking nice. And finally, in my opinion, a backyard coop should be good to look at.

Unfortunately yes...Prey

In a lot of residential areas, prey isn't much of a problem. In which case you can usually easily free range your chickens in your backyard. I say usually because birds of prey are out there. They'd have to be fairly large to pick up a chicken but...

And the other possible problem, Raccoons.  Add to that the regional hunters; foxes, bobcats, panthers.

Know your area and ask other chicken herders if they've had problems.