Manny,
My comment on the heat pump is that it may have some limitations, not saying it won't be what you want it to be. I have not personally used a heat pump in tampa to heat a spa in the winter, but have used gas. Here are what I perceive to be the limitations, and admittedly I may be wrong about this. My understanding is that pool heat pumps have a hard time creating heat for the water when the air temp is below 60 degrees, and below 50 degrees many don't even work at all. For a pool in your area that isn't too much of a concern-- you pump heat into the pool during the day when it's above 60 degrees, and if it happens to drop to 55 at night, your pool can still be 80 degrees. All is good. There is also a practical limit to how much hotter than the air the heat pump will make the water-- and as it gets colder that number goes down.
For your spa, the scenario may be different though. You may have different demands of your spa-- some people like to get in the spa in the evening, after a hard day of work. On colder nights in that area, you may not be able to heat the spa any more than it already is, so you'll have to heat it earlier in the day. And you'll have to heat it to a higher temperature than you desire and then it will cool down over night-- and as you've stated, you're not going to cover this spa, so it will cool down relatively quickly. This isn't the end of the world. What I'm saying is that on colder nights, your spa may not be over 90 degrees, and you may not be able to heat it up any further until the temperature gets back over 60. That may be fine for how you want to use the spa and the pool and for what you expect out of your heater and your water temperature.
As for the comment about safety--in your post from 1/13, in which you appear to paste in the specifications of your build, it specifically indicates that 45ft of fencing OR window alarms are included. My point is that you will need more than 45 feet of fencing to adequately fence that pool based on the dimensions you have provided. From your subsequent comments it's clear that you intend to properly fence the perimeter of the pool and have chimes on the doors leading from the home to pool area. I'm not suggesting that more than that is required, but it wasn't clear to me from your first description that you were planning to do this. There is a safety aspect to that, and also a budgeting aspect to it-- sucks to get hit with an extra $2k on the end of the project because they included 45 feet of fence, and you need a lot more than that, and you know that you're not the kind of person to leave it unfenced.
