what i would do in your situation, is find the exact line the sun travels over standing in your backyard, then find the spot that the most sunlight actually touches in a day.. shouldn't really be that hard. then just put your plant there... as for the watering thing, i haven't successfully grown a full marijuana plant yet, but i did used to garden as a hobby, too much water at one time could actually hurt it more then it not getting enough water... i would suggest a drip system rather then giving it one large watering before you leave and hoping for the best.