To answer your first question, you are better off using poly pipe. Because you live in an area where freezing is a concern, poly pipe is the way to go. Also, PVC pipe can actually be weaker and more brittle than poly pipe. Depending upon who designed your system, and what the water pressure actually will be at the heads, I would suggest 1" pipe. I wouldn't usually ever go anything smaller than 1". 3/4" pipe will create friction, and friction equals pressure loss, which is something you can't afford to lose. As for the funny pipe, make sure you push the funny pipe onto the barbs fully, other than that, it should stay in place. With your pressure, I would say I wouldn't go more than a couple of feet with the funny pipe.
Tony Posey
Ridge Run Landscapes