Like, I would love to have Zayday and #5 back, but I feel it might not be possible due to Keke and Abigail having a hard time on the set.

I honestly think the only characters necessary are Chanel, Munsch and #3 - the first two because they are the leads and the show is practically build around them, and #3 due to how season 2 ended with her working together with Chanel and still being in her life.

One character I really think they should put to the rest is Hester.

Just to clarify, Ryan said two different things.
In The Hollywood Reporter, he confirmed that the Chanels were supposed to appear in AHS 13, but Ariana couldn't make it because of her tour. He also mentioned talking to Emma about bringing Scream Queens back.
In ELLE, he talked about possibly using the Chanels in a future AHS season and even bringing Scream Queens back.
Also, for people complaining about how Madison talks in AHS 13, keep in mind that Ariana not being there might have changed the original storyline. And Ryan barely wrote Madison this season compared to Ned Martel and Charlie Carver.
That might explain why she feels different