have you seen this sample? it doesn't have any radio buttons, but it shows how you can define a renderer and apply it to a FeatureLayer on the fly.
its definitely a little trickier to create legends when you can't rely on the legend resource present in REST which uses the symbology defined for the service layer itself.
if you are hardcoding the renders in your own code perhaps the most straightforward solution would be to prebake the legend images you'd like to display.