Hello Lou, and welcome! I can't answer all of your questions, but I can tell you what I have learned.
1. Get a good test kit! The TF-100 is highly regarded here.
2. There are no stupid questions.
I have used an Intex SWG (here is a link to one of my posts -
http://www.troublefreepool.com/intex-swg-w-inground-pool-t8884.html)
As far as I know, SWG were first marketed for private swimming pools in Australia, and then spread around to the rest of the world. Ease-of-use features, size and brand names seem to determine cost. There are some experts on this forum who frequently provide much more details on the technical nature of the products.
From my experience, the Intex is almost perfect for me, but has its flaws - its connections are designed for Intex pools; loss of power=loss of program; program is just run time length. Those are far outweighed by its low cost(EBAY has several for less then $200 US,) and simplicity.
I can't tell you how long any of the brands cells will last, I don't even understand why they "wear" out(get so coated/covered with minerals that they are insulated?) PH rise with use a SWG seems to be common, but use of borates can slow it(works for me! :-D )
A feature that most of the high end models have is BOOST, SuperChlorinate, or Shock, which simply means that the unit runs for a longer cycle time. It will not generate chlorine any faster than normal, which in my humble opinion, is not fast enough to "shock", you should keep some fast-acting chlorine(bleach) on hand for that purpose.
The diagnostic features of some models look cool, and may be valuable to you; a clear cell so you can see it working, or tell if it needs cleaning; a salt level reading; water temperature; cell life time usage, etc..
The programming functions vary, but most are similar. I didn't see if you have a control system, but use of the same brand SWG is usually recommended.