Zim is intent on ignoring everything that was revealed in this episode, so theres no point in trying to explain anything.
Kind of, but not really, because Christian said there is no "now" where they were. Its just where everyone met when they died, and its outside of the laws of time for the living universe. Ben didnt go in because he wasnt ready to "let go" (probably waiting for Alex to 'remember' and go to the church), but everyone else found each other, which is what was holding them back from "moving on" to the afterlife the whole time they were in LA for the "sideways" flash.The "sideways flash" was more like a flash forward by hundreds of years.