Hey everyone, here’s a few answers to your questions:
You can keep fighting Zuul’Goth as long as you have the Sigils.
The week 
Gems.
Currently the timer is set to each day at daily reset (same as Guild Wars).
Only the Valraven will spawn. It will also be much higher and consistent for everyone across the event compared to the Gnome.
The hero isn’t limited by what class you’re using, you can use any class any week (or none!). 
You’re not penalised in so far that you don’t do less damage or get less points, but you won’t be able to use troops from other Kingdoms, no.
Raid Boss chest was possibly from an old screen shot? There is just the Rewards and Raid Boss Shop.
People can join the guild in the middle of the week and start participating in that guild’s efforts straight away.
Raid boss fights are individual, with the damage from the battle going towards a total to destroy a Portal.
More players present = more damage
It is reset with each event.