To best size your equipment you will need to know the inlet and outlet pipe diameter, approx. legnth of each pipe run then use a pump curve to determine the most efficient set up. For instance, the pressure drop between a 1 1/2 inch vs. 2 inch can cause a change in the pump size needed to circulate the pool within a certian time parameter. There's lots of info on doing these calculations available through the web to help. As a side note, my 15,000 pool (with solar and the larger pipe sizes works perfectly with a std. 1hp jandy stealth pump.

Can I assume that the 2" pipe diameter that comes out of the ground is the diameter of the run to the pool (which is long) and that a reducer wouldn't have been used where it attaches to the pool?

How would someone quoting the pool know any different than that, as well?

In my list, I also forgot to mention filtration. The last pool service suggested sand. Is DE not used with salt water?

==What size pump? I've read that larger pumps are more energy efficient* due to less run time *important to me ==

Actually a bigger pump is typically not a good idea for efficiency. Multi-speed pumps are all the rage these days because they can be set to run at a very low speed for efficient filtering and ramped up to higher speed to run water features or cleaners. Running a pump at low speed over a long period of time is actually more efficient than running one at high speed for a shorter time. You also don't want to turn the water over too fast because then you're not getting efficient filtering. And when you're running an SWG (salt water generator/ chlorinator) you generally run those 8-12 hours a day and they only operate when the pump is running.

==What size salt water system?==

Most are sized based on the gallonage of your pool. The Pentair IC20 would work for yours (handles up to 20k gallons).

==I've seen discussions about controllers and timers and I'm even more confused.==

Timeclocks simply turn equipment on and off at given intervals. If you've ever had a low voltage lighting timer with those little plastic clips that you put on the clock wheel for turning the lights on and off, it's the exact same thing but on a larger scale. Controllers on the other hand are software driven and allow you a much wider range of capabilities. It might help you to read through some of the literature for controllers on the Pentair web site (link below).

Here is a link that might be useful: http://www.pentairpool.com/