As far as water retention and well, etc. you may wish to think about what a "normal" size is, which may be considerably less than "full pool" to prevent loosing your sanity of trying to keep things at full pool. Water loss can be immensely frustrating, and based on the high desert comment, you are going to want the pond basin leak-free as much as possible. This means great compaction and possibly materials added to create a liner.
So if you set your mind to "normal" being 1 acre, but plan on the pond being as much as 3 when things are wet, you may have a better chance of meeting expectations. Excavate that 1-acre area deep enough to meet your goals, but plan your docks and so on for a great deal of water fluctuation up to the 3 acre mark.
It is too bad that gully nearby didn't run across your land, you could tap into that resource during runoff events.
