Both statements are untrue.
First, DOT 5 does not absorb moisture, so the boiling point is consistent, and does not damage paint, as well.
Factory proportioning was very poor and somewhere in Missouri is a bunch of kids that were on school bus in '95 that saw a dumbass in a '72 Dart try to pass, slam the brakes mid-pass, and swap ends. Thanks but no thanks, 9" drums.
Agreed but don't use alcohol to flush the system. It is NOT brake fluid, and absorbs moisture.
Agreed, but all brake fluids (that are DOT approved) are compatible. That's part of the DOT specification.
See above post.
OP, please don't put alcohol in your system. Either pull the components apart and flush and dry them completely if you're worried about it, or do what is designed; pour in DOT 5, pump till it bleeds purple, move on with life. It'll exist in the system fine, but they don't 'mix' together inside, so if you get a pocket of DOT 3/4 somewhere that has moisture in it, that can cause corrosion. Existing DOT 3/4 absorbs moisture, DOT 5 does not so....
If you're suspicious of your existing fluid, I'd flush with fresh DOT 3/4 first to mix n' flush with existing fluid, THEN start pouring the DOT 5.