I have Webstone ball valves that have a full port side that can be used for draining (3 way valve). I use them on my boiler as I can isolate all zones and then pressurize one side of bad zone if needed and drain from the other through a hose. This way no water dripping in odd areas. I have an air chuck > to garden hose fitting I use for draining sprinkler lines Same as using separate ball valve and boiler drain but more convenient, less connections and more $$. They come as NPT/Sweat/Pex.
Every house I know that has been built in the last 20 years here in SC and NC uses PEX and runs through the attic with standard foam insulation. IN our last community of 16 years it wasnt uncommon for some to have the pipe freeze in unusual cold temps in the teens. They just wait for them to unfreeze. Since PEX is flexible it doesnt burst like copper does.
Nothing is absolute but I wouldnt worry about it.
Not as much of an issue for cold water. Hot water maybe some. Heating pipes definitely.
I had this happen when I didn't know. I installed new HW baseboards in a bathroom conversion. I ran oxygen barrier PEX from boiler up to them since it was cheaper and easier. I put a long turn elbow about 30 feet away from baseboard to make a nice straight shot to boiler and that was braced against a ceiling/floor joist. It was about 70 degrees when installed. I fired up the boiler to test everything and check for leaks, baseboards get 180F supply. I went into that bathroom and the baseboard was 4" off the wall and bent the copper at the elbow at corner. I was like whiskey tango foxtrot and then did some reading and learning. Redid a bunch of things with copper, braced by baseboards and did some long PEX turns allowing for movement.
So I ended up ditching the heat tape idea, and started using these Freeze Miser devices. They drip when it gets cold automatically, which of course will also stop this pipe from freezing