I wouldn't worry about regen frequency, unless you start going over 20-30 days. There are those that will argue frequency, but unless you have really nasty (dirty) water, I wouldn't worry about it too much. My family's use means I will regen about every 5-18 days.

A 1.5 cu ft resin tank will allow better salt usage, as Tom and others have said; I went with one for that very reason. The price difference is negligible.

The rinse water will contain about the same chlorine as the incoming water; chlorine will remain in solution unless you remove it chemically, or unless it precipitates out once exposed to air. I'm not a pool expert, but I seem to recal reading somewhere that soft water is not good for a gunite pool...