ok, you have a total of 160 points to spend. you can have as many or as little units as you like aslong as you stay within 160 points.
Then there's all the rules about claxon counters and such and certain actions or movements set off alarms, increasing the claxon counter.
the defensive side has roving teams and probably one to defend the objective. if you get too close or set off a certain claxon, a unit will respond. however, if one unit responds, the others may not, it depends on location and such. so even if you're spotted, you arent instantly up shit creek without a paddle.
thats about the extent of my knowledge, someone with better understanding is bound to answer.