Ok after John hears the words “Come up here”. The church is not mentioned again.
No need because John went into revealing what was going to happen. No need to mention any churches anymore since he said all he had to to the various churches.
Not named specifically, but is present in chapter five as a category identity (just like David used when assigning family participants in the Temple services) when the L:amb takes the scroll and begins opening it. Four and twenty elders is a category identity not specific individuals.