Coming off and staying off for a decent amount of time is and should be just as important to you as when you're on cycle...your body needs a break and it needs to "normalize."
16wks is a good solid cycle and is just about the perfect length IMO to get the most bang for your buck. Yes, you can stay on longer, and yes, I've stayed on a good deal longer then 16 wks, but from my experience 16 wks cycles with maybe the occasional 20wk cycle is about the limit you should push it.
As far as time off, most will argue that time off should equal time on. There is nothing wrong with this way of thinking and in truth, it is the easiest way to ensure that your body remains in a positive functioning routine. This does however not mean that you have to follow the time on=time off approach, you can get by with less time off, but if you do that you really need to make sure everyting in your body is in proper order, i.e. get your blood work done, checking liver values, cholesterol, blood pressure, etc. If you do this and everything checks out OK, then it is probably safe to say that you could jump back on, but again, everything needs to be in proper working order, and the only way for this to occur is to take the time off that your body requires...which can be like everything else, very individually based.
