Personal items. Good choice on the 5' max depth. Our PB suggested 5' but my wife wanted 6', which turned out be a mistake. I want to be able to stand on the bottom anywhere--to rescue a kid (we don't have any at home) or for maintenance, plus it turns out most people do want to stand in the pool, so now the deep end is less used.
Sun shelf. For us that turned out to be a huge waste of pool area. We have
never used it. Sunning is so 20th century. If I want cancer, I'll just start smoking. Instead of the sun shelf, I wish we had just done full width stairs for lots of multi level seating.
Air blower for the spa. We have a Silencer 2 hp, and it is simply too powerful and splashes water out of the spa like crazy. I called the manufacturer of the blower, and he advised a 1 hp would probably have been better, but now, since the blower is on top of a big PVC pipe he suggested drilling some 1/4" holes in the pipe to bleed off the excess air. I have maybe ten holes at different heights and positions around the pipe, and that has tamed the problem. If I change my mind, I could just tape over the holes or even put screws in them, but so far that's not likely to happen, although if I have to replace the motor, I'll get a 1 hp and cover the holes.
Spa layout. We have about a five foot spillover. I would have gone narrower than that since we typically run the pump at about half speed. Also the seat in the spa does not go all the way around--it stops where the spillover is. I would have it run the full perimeter of the spa.
That's it. Here in the Houston area we use the pool from mid April to November but the spa 12 months, since I can set the suction and return valves to isolate the spa, making it easy to heat it up in just a few minutes in January. However we didn't use in the middle part of February this year, but the icicles on the spillover were fun.