I put one in over 10 years ago...

18x36 with like a half moon spa feeding into it. Shared heating and filtration systems unless you want spa mode, in which case the waterfalls from spa to pool stop and the heater focuses on the spa.

Auto cover very nice feature. Keeps dirt out, heat in (maybe not a benefit for Southern CA). It also is a very nice safety feature in that you can walk on it (i.e. no young kids can get in if it is closed). Also have in-floor cleaners, which basically do everything for you. We have people open and close it and weekly chem checks, plus then whenever a pump or something dies. Given we are over 10 years now we've replaced a lot.

Our backyard was previously unusable in summer due to southwest exposure, even in Illinois. Sweltering. If kids are the right age, adding a pool is a major plus.

Get some good multi-colored lighting, too (you can select any color you want or have it continually scroll through). Adds a ton at night. Depending on depth consider a slide. Also we have a b-ball hoop "built in" to the walkway around the pool (two bars hold it very sturdily in place but can be removed in winter).

Regarding chem checks I had never wanted to invest the time and effort into becoming independent on this but I'm in the midst of changing pool companies so now might be the time. Still would have to hire for opening and closing and major repairs.