I live in downtown Toronto and use my Airsoft guns for target shooting all the time. Set up a good sized back stop (mine is about 2ft x 2ft) and try to match the gun and target so the BB penetrates rather than bouncing off. I've shot gas pistols, spring pistols, gas rifles, and electric rifles at speeds ranging from 200fps to 550fps. My distances range from 15ft to 30ft and airsoft guns are plenty accurate enough at short ranges like that. My target sizes are between 1/4in and 2.5in and material is either paper, cardboard, a gel trap, or metal (beer cans, pop cans, and cat food cans) depending on the gun. I wouldn't consider the risk of someone looking in the window and calling the cops any higher than if you were shooting a dart gun or a squirt gun inside.
I've loved target shooting since I was a kid but pellet guns are way too dangerous to shoot in my apartment so this airsoft stuff fits the bill perfectly. The ricochets can be a problem but the bigger problem if you do it often is you'll find BBs *everywhere*. Those little buggers have a habit of working into the strangest places and no matter what backstop you use there's always a percentage of BBs that don't get trapped.