Writing a series, and dealing with fan expectations.

Hi all.
This post is one I've wanted to write for a while, but it's only since writing my latest work that it's actually started to effect me.
I started writing back in 2014, and wrote my first book, Souls of the Never, in three weeks on an android tablet, did a really crappy cover up on Canva, slapped it up onto KDP and sat back, waiting for the millions to pour in.
Wanna know what happened? I'm sure you already do, but it was nothing. I sat for days in frustration, wondering why people weren't buying this book that I'd poured my heart and soul into.
And, yes, I was one of those 'BUY MY BOOK,' spammers. I didn't know any better. I hadn't done my homework, had no support network in any of the author groups, nothing.
But did I give up? No. I started book two in the series, while at the same time actually looking at how the book/author world works. I joined groups, took part in conversations, helped people out with proof reading etc, and guess what happened next?
I got a pm on Facebook from this lovely lady in New Zealand, who after introducing herself proceeded to tell me how crap Souls of the Never was. I agreed with her. She wasn't shocked. She'd been following my posts, had seen I was one of those authors who could take criticism, and actually wanted to learn and improve.
So, we spent six months licking Souls into shape, and while I proof read a few of her books(and actually ended up appearing in one), at the end of it I had three books of the series complete, plus a novella prequel.
Now, I won't say they are perfect by any stretch of the imagination, but thanks to the writing community and their feedback and assistance, they are a HELL of a lot better than they might have been.
I suppose it was a blessing in a way, as by the time the series was available was when I felt comfortable enough to start marketing, and this is when it started to sell.
I actually have FANS! People who have contacted me to tell them how much they love my characters, people who have reviewed(both good and bad lol), even people who send me random(usually dragon-related), gifts.
But this was all great. They were happy as the series was all there, and they could read one and carry on to the next without having to wait.
This is where it gets tricky. I've just finished book one of my new dark fantasy/horror novel, Treaters, book one in a new series. The launch went really well, so much so I have readers contacting me asking/demanding me to start book two.
My dilemma is I have another book one of another series in the works and almost finished, so I have to decide what to do. Do I finish the other book one? Do I get Treaters 2 started? Do I do both, and if I feel especially masochistic, start writing the three novellas set in the Neverwar universe I have lurking at the back of my brain?
These are the struggle of an author, but you know what? I wouldn't change it for the world :)
I love my readers, and want to thank you all for making this such a humbling experience.