Roughly 9 seconds give or take and based on the game heartbeat.
That sounds like it will be a choice for you to make. Whether you want to build to max damage before using your cries and calls or not is really a choice for you to make.
Incorrect, but an easy misconception to make. Ballads can be replayed as often as you want and they do deal damage. You have 2 new cries. You have better survivability due to Noble Cause (trust me, there is a nice boon there for Harmony/Power of Song trait lines), if you use the armour of song trait you also have a little better survivability. The bubble defence reduction comes with an added ability to remain relevant longer because there is far less power drain.
Sounds like you are soloing here, maybe join a fellowship so you are in combat with your fellows? It's a thought, again though you get roughly 9 seconds out of combat.
1. Same as they do in live.
2. The tail on buffs lasts roughly 9 seconds.
3. Cry of the Chorus still exists. Your skills are all available, except for Anthems and the Coda until you use three ballads. Ballads are on a 1 second cooldown and can be used over and over as they can be in live.
4. Cry of the Chorus doesn't deal damage. It buffs you and applies 3 ballad buffs, unlocking Anthems and Codas.