I think the main question is not 'how much is enough' but 'how much is too much' or 'when to stop.' And the answer to that is, if it starts smelling like ammonia or other unpleasantness, that's a sign that the limit has been reached as far as the amount of nitrogen the pile can absorb.
So 'stick a fork in it' now and then to check the conditions. You should do that anyway if you're adding a jug at a time, just to make sure it's evenly distributed and doesn't run through and out the bottom, leaving untouched dry parts.
Re: 'exposure', there is none after dark. Just sayin'.