Will low well water pH cause plumbing damage or health problems?
A pH of 6.0 is not unreasonably low for a well-water system.  That's at the low end of the "normal" range but not anything I'd worry about.

Copper pipes will not be "dissolved" at this pH level and the minute amount of Cu that you are consuming is not a concern.  It's a common mineral and it is not generally harmful to humans, certainly not in the quantities you're talking about here.

I'm sure the installer you talked to has a solution to this "problem" and he's trying to sell you one.