I live in a condo (40ish yo) and recently a neighbor in an adjacent building had a leak and the board suggested that everyone have a plumber come inspect their units. I just inspected and found various levels of corrosion at most joints with the included photo the worst looking of the bunch.
How concerning does this appear?
I’m guessing it’s blue because there is a decent amount of sulfur in the water which is forming copper ii sulfate around the leaking joints.
I think you’re spot on about everything else though. Rip this out and replace with new connections.