No, you are not doing okay as long as you stay above 12 volts. Most healthy batteries will be above 12 volts when fully charged, and an alternator is ideally bringing your voltage up to 14.4 when the system/vehicle draw does not exceed the output of the alternator.
I assume we are talking about a daily system, as opposed to a competition system where you are trying to maximize the output to tenths of a db. In the case of a daily driver system, basically as long as you never need to use jumper cables to start your car, its sufficient. This is because everyone's listening habits are different. How often you play the stereo while the engine is on, how loud you play it, and even (sometimes) the genre of music you listen to can affect the average-over-time draw your system puts on the charging system.