<<1. Is it possible to use chord symbols like in Sibelius? (Ctrl+K)>>
Nope, Daniel stated in another post that chord symbols would not be in this, or the next, update. Apparently it’s quite a trick to program it correctly and they don’t want to rush it. It’s a much bigger feature than might appear to the untrained eye. Er, ear?
As to what the exact keyboard shortcut will be, that’s anyone’s guess at this point.
<<2. Will it be possible to hear the chord playing when you insert the symbol?>>
Also unknown. However, you can already hear a chord when you click it in the Write Mode in the new version upate.
Chord symbols are probably a huge headache to program, especially because people need them to transpose accurately with the transposition of the notation. And once chords are implemented, people will want slash notation along with accurate transposition of the chords symbols.
I’m glad that Daniel and the team are taking their time with adding the chord capability to Dorico - we can manually type non-elegant chords into the music using text, so we can currently produce rudimentary lead-sheets if we wish. As Phrazemaster suggests, I agree that programming chords correctly so that they satisfy the majority of users when first introduced is probably a huge headache and very very complex.