Use only one notification for all events
The normal android application must notify only one time by application. Else, a big list of notification are showed. I think it's may be a good idea to present only one notification with all informations.
But those are not the same information. Some users stream their episodes, other download just a few episodes not all of them, so those notifications make sense.
FYI you can disable the notification you don't need in settings/notifications
I think you could. You could have a single notifications where you have different actions, such as go to the playlist, download manager,play. I think this would cover most situations.
Every other day I wake to two notifications that are basically the same, there are new podcasts and the app has downloaded new podcasts. the information is the same. The only thing different is the title.
I'm not sure about any guidelines talking about a single notification per app. In case of Podcast addict that won't be possible. Some notifications must be displayed on their own like the player notifications. Others when pressed open different screens so I don't think merging all of them will be useful.