Need help with DIY solar

[Stew]

Hello all.

I'm new here so please forgive some of what may seem like simple questions. I've been researching this for a week and can't find some of the answers I'm looking for.

I am in the middle of designing a solar system for my small inground pool. I am located in the Mayan Riviera in Mexico. Our swim season is usually around March to Oct. with unheated pools depending on the weather. Winter freezing is not an issue. In the summer, my pool is around 30C-32C (86F-90F) and gets about 5, maybe 6 hours of sun per day. With that information, here are my questions:

1) With freezing not a factor, do I need a vacuum break on the panels? I don't want them to drain if not necessary in order to work on the pump upon startup.

2) I am planning on making coil type collectors using polyethylene pipe. I calculated 10' head due to friction loss threw 200 feet of 3/4" pipe (1 collector). If I use 5 collectors, is the dynamic head 5x the single collector or equal to it? This is unclear to me given what I've read.

3) If the recommended flow rate is 5gpm threw the collector, I need 25gpm total threw the bottom manifold in order to supply this flow rate to the five collectors. Is it better to use 1-1/2" pipe or 2" pipe for the manifolds? The rest of my pool plumbing is 1-1/2".

4) Currently, I have a single speed 3/4hp pump. My current setup turns the pool over in around 5 hours. Based on my total dynamic head calculations, this pump should be producing around 25gpm based on it's performance curves. Assuming this pump is sufficient to get the water on the roof (about 20' vertical), and given the siphon effect of the water coming down off the roof, would it be better to have a two speed or variable speed pump, higher speed to lift the water, then lower speed to circ. the water and save energy (electricity rates are crazy here)?

If you could help me out with this it would be greatly appreciated. I want to do this right the first time.

Thanks in advance.
Dave