For the first few years I wrote historical romance books that followed the same Scottish family from generation to generation. They sold very well, but after some 30 books, I was sick of them and couldn't come up with more plots.
So, I switched to contemporary romance. It's like starting all over again. My readers didn't convert well.
For those starting out, keep that in mind. If you choose a specific genre, you might get stuck with it.
My original idea was supposed to be 6 books, then I had a totally different idea to move on to. I'm still doing the original idea 50+ books on, and the different idea is still only an idea. The wonder is, the ideas keep coming, and the fans keep demanding more.
The last book out there didn't have a good release, because it shifted into contemporary fantasy for the first time, and was shorter. But it's actually sold almost up to expectations anyway, so all I missed out on was ranks. The goof I made was not making it clear it was in the universe and something of a prequel. But once that was cleared up, partly by a cover change, and then by reviews, it's done fairly normally.
But yeah, you need to really like writing the genre you start with, because changing it can go over really badly with fans. Mine like me changing it up as long as the continuation is there, but a real genre change on something that looked different took a big release day hit.