Probably the more the better, as when conditions are lacking, you won't generate much. Generally speaking, you could "get away" with 100 but it is always nice to have more, so if the 160 will work do it. I like the grape solar folks, and their warranty is good. No hassles. There is someone from GS on the forum here, but not real active.
The reason I said not MPPT is because they generate a lot of RF interference, I noticed it particularly with HF ham, but if it does not cause you any problems, don't be too concerned.