It sounds like a comical piece.
But the funniest things are funny because they're true... so try to anchor as much of the humor into what people who believe in Purgatory would expect. So the first thing you need to do is decide if you're doing a Christian version of Purgatory, or an Islamic version of Purgatory (
Barzakh), or a
Buddhist version of Purgatory, or whatever.
For example--- from the Christian perspective-- Purgatory is a process, more than it's necessarily a specific place. The purpose of Purgatory is to rid us of the things that still separate us from God and prevent us from being in heaven-- because nothing unclean can enter Heaven. So you've got the pain of purging yourself of your attachment to wrong-- but you also have the joy of the knowledge if it being a temporary inconvenience, with something good at the end of it. From the Christian perspective, you get two judgments-- the first is after your death, where your heaven/heaven-but-first-purgatory/hell is determined (aka, being open to God's love/being open to God's love, but you need to break down your own barriers that are preventing you from fully accepting it/rejecting God's love); and the second one happens when time is finished, so that everyone can see the full repercussions of your actions that traveled beyond your own lifetime.
So, that said, it's very plausible to serve your Purgatory on earth, where you failed to do what you were supposed to be doing during your life. So, for example, a harsh and discouraging teacher might serve their Purgatory in their former classroom; or a neglectful mother might serve her Purgatory amongst her grandchildren who are now being neglected, because she never gave her own kids a good model for being a good parent. So if you think about it in terms of punishment-fits-the-crime, it should be pretty easy to figure out who needs to go where.
As far as preparing the living locals-- how much interaction do humans have with the supernatural in your world? Is it limited to just seeing ghosts, ho-hum, a new one has moved into our bedroom--- or are you throwing in other stuff as well? (Angels, demons, souls, etc.) If you're using a theological concept for your story, then it shouldn't be jarring to have it announced from the pulpit-- "Oh, by the way, you might be noticing an uptick in ghosts in the neighborhood... it's because blah, blah, blah, so make sure you blah, blah, blah, but don't blah blah blah..." And in the pews-- "Um, where did he get that announcement from?" Or perhaps there might be an odd advertisement run in the local newspapers, but no one quite remembers how it got there. Or pertinent people's cellphones might get spammed with a series of message blasts, and the FCC has no idea who sent it... etc. Lots of ways to spread information, but it depends on how you want the scene to play...
So, as far as the fictional command structure, going back to the judgment scenario, it's basically you + God in that scene (some say that your Guardian Angel stands by you as well). Jumping to the Purgatory part, some people say that your Guardian Angel will visit you in Purgatory, but mostly you're by yourself, working on fixing what's keeping you from being the perfect You. It should be easy to add in some middle-manager bureaucrats who get you to where you're supposed to go, some other bureaucrats who get you settled in, and some other bureaucrats who check your progress. Perhaps the interactions they have with the living give them progress in their path, and allow them to compensate for their shortcomings during their lives, or correct the repercussions of their own initial errors. Or whatever. But if you think of the positions as a combination of government org chart + hotel org chart + self improvement, that might do something.
Good luck!
