20 to 25 max. I personally see trigger words as a starting point many of them quickly become redundant as you start forming questions and other words become more significant as you activate.
Since the mind can only really hold 5 to 9 bits of information more really isn't better. For a Minimum I recommend 8 depending on your writing speed 25 really is the maximum achieve able with the fastest scrawl considering the page flipping and decision making and questions you start forming already.
Alex
