1. Increasing evaporation increases the volume of Kalkwasser you can add via water top off means. Adding vinegar to your Kalkwasser mix increases the amount of dissolved calcium hydroxide essentially increasing the amount of calcium ions in a given volume. They are different mechanisms.
2. The instructions suggesting telling you not to mix more than a gallon of Kalkwasser at a time are becuase of concerns that Kalkwasser can "degrade" over time. That may not be as much of a concern as once thought. Read this article:
http://reefkeeping.com/issues/2003-0...ture/index.htm
In my previous system I used a 10 gallon photo lab chemical storage tank with a floating lid as my reservior. That was connected directly to a float valve. Once a week I would add more RO water and Calcium Hydroxide stir and let settle again. (I had a shut off valve so that the Kalkwasser wouldn't be delivered untill the undissolved Kalkwasser had settled to the bottom.
About every 2-3 months I thouroghly cleaned the reservior and float valve.