You may be focusing too much on getting down to 12 pounds. You will get stronger as you hike along on a long trip. That extra pound may not seem so much. And the amount of water you will need will partially depend on weather. If it is cool, you will need less water. Is it possible to time the trip so that the dry sections will conincide with cool weather? How about the old trick of hiking in the early AM, nap mid-day, and hike in the cooler evenings? Or plan the dry sections when there is a full moon and travel at night? You do need adequate water but there may be strategies that will reduce your water needs. Water truely is your heaviest item.

I agree with others, that skip the luxuries and any extras - be minimalist and get the lightest stuff available. It has been my experience that it is also good to be flexible and not over-worry. On long trips, after a week or two the comfort of the sleeping pad is not that important to me- the more important factor is its insulating warmth. Humans are very adaptable. Once you feel really at home on the trail, you may think differently about what you need.