vaderios said:
What if:

1.Instead of the executor and all the fleet suddenly arrives from nowhere having them jumping out from hyperspace.

We'd have to change the Emperor's line about moving the "fleet to the far side of the Sanctuary Moon. There it will stay.... until called for."

2. The rebel fleet is near sullust. Can we see the system/planet on the ship concentration?

I don't see why not. But they are massing NEAR Sullust, not AT Sullust, so it's not necessary.

3. The death star have a more impressive/extented explosion aka what Darth Venal posted as Alderaan's destruction?

It would be awesome if it fell apart in huge chunks instead of popping.

4.

Very yes.