I have been using black poly coils for the last three years.
Basically just blow as much water out as I can, the pipe can take a bit of stress, but 90% of the water out there is lots of room for the ice to expand, have yet to have troubles with freeze up out here in the west, Alberta.
When I first started out I used a small Intex pump to circ, my panels are on the ground so head pressure wasn't a big deal, I also used to run a check valve to prevent them from draining. Since I have gone to a 2500 gph 3/4 hp pump dedicated to my heating circuit I haven't worried about the panels draining back as the pump just pushes the air out when it starts up.
Next year I plan on adding more coils and running a large header to feed all my coils individually, coil length will be around 100', each coil will have an isolation valve on the feed. Then to balance the system I will buy a temp sensing device/gun for about 50$, then adjust the valves so I get even output temps on the pipe, just in case anything decides to take a short circuit on me.
The last few years I have been using an old heat/cool thermostat mounted inside the enclosure I have my coils running in, this controls the operation via a 24 volt transformer and 24 volt valve. Having two heating circuits one solar and another a heat exchanger my "heating" pump runs whenever my filtering pump 1 hp doesn't, so I cycle the solar with a t stat and the heat exchanger circ pump with a timer.
One important thing I did learn here and poolside this year is sq footage is very important, my coils/exchanger worked good on my 16' pool last year not so good this year with a 24' pool, more square footage to come next year.