In answer to your 1.:
It used to be possible to select chord symbols when selecting notes. This behaviour was changed because it made it very easy to change or delete chord symbols when pasting over existing material (with existing chord symbols). This isn’t an apparent problem if you only have chord symbols showing in one part, but if you have them showing above multiple players you’ll see that if you change one chord symbol, they update in all other players automatically.
In Sibelius if you copied over existing chord symbols in one stave it was very obvious, because the staves above and below wouldn’t change.
In Dorico you can of course use your mouse to perform a marquee selection (which is easiest in Galley view) or select all and filter chord symbols.