Some of my bikes let me ride no hands, others don't. I know it's the bikes because I still have some of the same bikes I used to ride hands-free as a youth and they still work fine. Its easy to test by moving your hands about 1" from the handlebars.

Looking back is an acquired skill. One important thing is that when you turn your body, your arms( not your hands ) have to be looser on the handlebars so that as your body turns, you are not inadvertently pushing and pulling the handlebars. So I lean forward slightly before looking back. I don't look back with only one hand on the handlebars. Having both hands on the handlebars, gives me the feedback that I need to maintain a straight course. Having only one hand on the handlebars while looking back, is definitely a recipe for disaster. It's almost like riding with your arms crossed on the handlebars.

The easiest way to practice is to sit in your desk chair with your finger tips on the desk. Then turn and look behind you. Feel how your arms flex. Then when you feel conifident, find an empty parking lot to practice in.