Actually there is no audience limits for podcasting. A standard license is always fine.
@Mib4Mio, is the music you used PRO registered? I wonder what Spotify means by the music not being podsafe. Envato used to advertize (maybe still does) their music as being podsafe. I can’t think of anything, other than the music being registered with a PRO, that could have changed this status. In any case, this is a very interesting question, the answer to which, may have some repercussion for us authors.
As for your second question, if you have more than 52 episodes you need to get a new Standard license for the additional episodes.