What percentage of your listeners would you consider your "core fans/listeners"? They listen to every episode, want community, etc
Hard to say indeed. For the community I created https://www.journalduhacker.net (kind of hacker news in french, 5 years old), we are currently 3 core contributors (also moderators), maybe 20+ very regular contributors, and 100+ punctual contributors. I think we can consider thses three categories as core fans.
Did you build this as a community for a podcast?
I wonder if there are podcast analytic tools with retention charts.
Would be great. I don't know of any :/
It's hard to say! For the most part I have no clue who's listening to the podcast, and I'm not quite sure how others find out. I suppose you can do surveys, but there's going to be some heavy selection bias, which makes it difficult to extrapolate.
The core user concept is virtually unknown in podcast audiences... It's crazy. Every other product relies heavily on this concept.