What you needis to understand which terminals on the radio itself are for
+/- 12 volts, Right +/- speaker and Left+/- speaker leads. Low voltage so
not a fire hazzard. Sound will be as good as you'd want if you've found a
reasonable radio and good speakers.

Not always as safe as you'd like. I've had a car radio set the
dashboard on fire when the alternator was screwed up and spiking
higher than the noise-suppression coil could cope with.